Hate ^allege of JVgricultutc
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Cornell University Library
TN 775.R55 1896
Aluminium; its history, occ"''* "SiPmSP^
3 1924 003 633 751
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ALUMINIUM.
ALUMINIUM:
ITS HISTORY, OCCURRENCE, PROPERTIES,
METALLURGY AND APPLICATIONS,
INCLUDING ITS ALLOYS.
BY
JOSEPH W. RICHARDS, A. C, Ph.D.,
INSTRUCTOR IN METALLURGY AT THE LEHIGH UNIVERSITY.
\
THIRD EDITION,
REVISED AND ENLARGED.
ILLUSTKATED BY
f . .
FORTY-FOUR ENGRAVINGS AND TWO DIAGRAMS.
PHILADELPHIA :
HENRY CAREY BAIRD & CO.,
INDUSTRIAL PUBLISHERS, BOOKSELLERSi, AND IMPORTERS,
No. 810 Walnut Stbebt.
LONDON :
SAMPSON LOW, MARSTON & CO., Limited,
ST, dunstan's house, petteb lane, fleet stbeet,
1896,
TH115'
(5 13% S^
COPYEiaHT BY
JOSEPH W. RICHARDS,
1895.
Feinted by the
WICKEESHAM PRINTING CO.,
63 and 55 N. Queen Street,
Lancastek, Pa., U. S. A.
l>e&icatlon.
TO THE MEMORY OF
iFteberick Mobler
OP
GOTTINGEN,
THE DISCOVERER OP ALUMINIUM,
AND OF
Ibenti Sainte^Claite Seville
OF
PARIS,
FOUNDER OP THE ALUMINHJM INDUSTRY.
THE FRUITS OF WHOSE LABOBS
HAVE ENBICHED SCIENCE AND BENEFITED MANKIND.
PREFACE TO THE THIRD EDITION.
Ten years ago aluminium was an almost unknown metal;
then it sold for twelve dollars a pound, now it is bought for fifty-
cents ; then the yearly production was less than is the present
daily output ; then only three books had been written about it,
since then seven have appeared and two journals have been es-
tabHshed to represent it. The lowering of the price, the increased
production, the wide circulation of reliable information about
aluminium, have brought to pass the dream of Deville, for it has
truly become a metal of every-day life.
The abundance of aluminium in nature, the purity of its ores,
its wonderful lightness and adaptability to numerous purposes,
indicate that the goal of the aluminium industry will be reached
only when this metal ranks next to iron in its usefulness to man-
kind.
To assist this consummation by furnishing all the reliable in-
formation about aluminium, to thus enlighten the general reader,
help the workman, instruct the student, assist the experimenter,
and in every way to speed the industry on its destined path,
is the raison d'etre of this work.
The writer thanks the public for its generous appreciation of
his past endeavors. The volume has been revised to date, sev-
eral chapters have been largely re-written, and every effort has
been made to make the work worthy of the splendid industry
which it represents.
Joseph William Richards.
The LEfflGH University,
Bethlehem, Pa., October zj, iSgs-
(vii)
PREFACE TO THE SECOND EDITION.
If it was true that no apology was necessary in presenting a
work on Aluminium in English, as stated in the preface to the
first edition of this book, it is equally true that still less apology
is necessary in offering an improvement on that work.
The present volume is designed to be an improvement on
the former one in the following respects : Mistakes have been
corrected wherever detected by the author or pointed out by
his friends ; in some instances the order of treatment of different
parts has been revised, so as to bring them into strict, logical
sequence ; the more strictly historical processes are described in
greater detail, in order to preserve a complete record of the rise
of the aluminium industry; chapters have been added treating
on the properties and the preparation of aluminium compounds,
on the theoretical aspect of the reduction of aluminium com-
pounds, and on the analysis of commercial, aluminium and its
common alloys ; the original chapters have been in several cases
sub-divided, and every part treated more by itself and in greater
detail than before ; finally, additions have been made through-
out recording and describing the progress achieved in the last
three years, with a completeness which it is hoped is up to the
standard of the rest of the book.
The method of treatment in the present edition will be found
to be more critical, for wherever a reasonable doubt might be
expressed as to the correctness of certain claims, or a rational
explanation advanced for certain phenomena, the author has not
(ix)
X PREFACE TO THE SECOND EDITION.
hesitated to put his best thought on the question and to state
his conclusions unreservedly.
The friendly criticisms of the scientific press and their sug-
gestions have been kept in view in preparing this new edition.
The spelHng " aluminium " has been retained, because no suffi-
cient reasons have been advanced for changing it to " alu-
minum;" and even if each way was equally old and as well-
sanctioned by usage and analogy as the other, the author's
choice would be the longer spelling, as being more euphonious
and agreeable to the ear.
It has been the author's endeavor to make this volume as
complete as possible, as accurate as possible, to write it in a
manner which will be entertaining to the general reader, and to
furnish a treatise which will be of practical value to the practical
metallurgist, as well as of scientific merit where it touches on
matters of theory.
J. W. R.
Bethlehem, Pa., March 12, i8()o.
PREFACE TO THE FIRST EDITION.
No apology is necessary in presenting a work on Aluminium
in English. In 1858 Tissier Bros, published in France a small
book on the subject. H. St. Claire Deville, the originator of
the aluminium industry, published a treatise, also in French, in
1859. Deville's book is still the standard on the subject. Until
December, 1885, we have an intermission, and then a work by
Dr. Mierzinski, forming one of Hartleben's Chemisch-Technische
Bibhothek, which is a fair presentation of the industry up to
about 1883, this being a German contribution. Probably be-
cause the English-speaking people have taken comparatively
little hand in this subject, we find no systematic treatise on
aluminium in our language. The present work aims to present
the subject in its entirety to the English reader.
Tissier, Deville, Mierzinski, and the German, French, and
English scientific periodicals have been freely consulted and
extracted from, full credit being given in each case to the author
or journal. As this art has of late advanced so rapidly, it has
been a special aim to give everything that has been printed up
to the time of publication.
The different parts of the work are arranged in what seemed
their logical order, corresponding closely to that followed by
Deville. The Appendix contains an account of laboratory ex-
periments, etc., several of which, it is trusted, may be of value.
In conclusion, the author wishes to thank the Faculty of his
" Alma Mater," Lehigh University, for their permission to use
(xi)
Xli PREFACE TO THE FIRST EDITION.
his Thesis on Aluminium as the basis of this treatise ; also, to
acknowledge his indebtedness to Dr. Wm. H. Greene, of Phil-
adelphia, for assistance rendered in the preparation of the work
for the press.
J. W. R.
Philadelphia, November 2j, j8S6.
ABBREVIATIONS DSED IN MAKING REFERENCES.
SEPARATE WORKS ON ALUMINIUM
{Arranged chronologically.^
Tissier . Recherche de 1' Aluminium. C. & H. Tis-
sier. Paris : J. Hetzel et Cie. 1858.
Uhlenhuth Die Darstellung des Aluminiums. Ed. Uhl-
enhuth. Quedlinburg: G. Basse. 1858.
Deville De I'Aluminium. H. St. Claire Deville.
Paris : Mallet-Bachelier. 1859.
Mierzinski . Die Fabrikation des Aluminiums. Dr. Stan-
islaus Mierzinski. Vienna : Hartleben's
Chemisch-technische Bibliothek. 1885.
Richards (ist Ed.) Aluminium. Joseph W. Richards. Phila-
delphia : Henry Carey Baird & Co. 1887.
Richards (2nd Ed.) Aluminium. Joseph W. Richards. Phila-
delphia : Henr}' Carey Baird & Co. i8go.
Le Verrier Note sur la Metallurgie de I'Aluminium.
U. LeVerrier. Paris: BaudryetCie. 1891.
Minet L' Aluminium. Adolphe Minet. Paris ; Ber-
nard Tignol. 1892.
Lejeal L'Aluminium. Adolphe Lejeal. Paris: J.
B. Bailli^re et File. 1894.
TREATISES IN ENCYCLOPEDIAS.
Fremy Enclyclop£die Chimique. Fremy. Paris :
Ch. Dunod.
Art : L'Aluminium par Margottet (1883).
Art : L'Aluminium et ses Alliages par Wick-
ersheimer (1890).
Kerl and Stohman Enclyclopadisches Handbuch der Tech-
nischen Chemie. 4th Ed. Brunswick :
Vieweg und Sohn. 1886.
Art: Aluminium von R. Biederman.
Watts Watts' Dictionary of Chemistry.
( xiii )
xiv ABBREVIATIONS USED IN MAKING REFERENCES.
JOURNALS AND PERIODICALS.
Ann. de Chim. et de Phys. . . Annales de Chimie et de Physique.
Ann. der Chem. und Pharm. ) Liebig's Annalen der Chemie und Phar-
Liebig's Ann J made.
Bull, de la Soc. Chim Bulletin de la Soci^t^ Chimique de Paris.
Chem. News The Chemical News.
Chem. Zeit. . . Chemiker Zeitung (Cothen).
Compt. Rend Comptes Rendus de les Stances de I'Acadd-
mie. Paris,
Dingl. Jrnl Dingler's Polytechnisches Journal.
E. and M. J The Engineering and Mining Journal.
Jahresb. der Chem Jahresbericht ueber die Fortschritte der
Chemie.
Jrnl. Chem. Soc Journal of the Chemical Society.
Jrnl. der Pharm Journal der Pharmacie.
Jrnl. fiir pr. Chem Erdmann's Journal fiir praktische Chemie.
Mon. Scientif. Le Moniteur Scientifique. Dr. Quesnesville.
Phil, Mag The London and Edinburgh Philosophical
Magazine.
Phil. Trans ... Transactions of the Royal Philosophical
Society.
Pogg. Ann Poggendorff's Annalen.
Poly. Centr. Blatt Polytechnisches Central-Blatt.
Proc. Ac. Nat. Sci. .... Proceedings of the Academy of Natural
Sciences (Philadelphia).
Quarterly Journal Quarterly Journal of the Society of Arts.
Rpt. Brit. A. A. S Report of the British Association for the
Advancement of Science.
Sci. Am. (Suppl.) Scientific American (Supplement).
Wagner's Jahresb Wagner's Jahresbericht der Chemischen
Technologic.
Zeit. fiir anal. Chem Zeitschrift fiir Analytische Chemie.
JOURNALS REPRESENTING THE ALUMINIUM INDUSTRY.
The Aluminum World .... New York. Published monthly. Estab-
lished September, 1894.
L'Aluminium Paris. Published monthly. Established
January, 1895.
CONTENTS.
CHAPTER I.
History op Ai<uminium.
'page
The alumen of Pliny; Alumen Roccae or rock alum; Alums and vitriols
confounded .... ....... 1
Paracelsus distinguishes alums from vitriols; Views of Ettmiiller, Stahl,
Hoffman, Geoffroy, Hellot and Pott, on the nature of the base of
alum; Marggraff's dissertations on alum and its earth; Morveau fixes
the nomenclature of alumina 2
The search for aluminium; Macquer's supposition; Baron's attempts to
reduce alumina; Lavoisier's views on the nature of alumina . . 3
Ruprecht and Tondi's experiments; Criticisms of Savaresi, Klaproth
and Karsten; Dr. Hare melts alumina without noticing any reduction;
Sir Humphry Davy attacks the earths with his great battery . . 4
Davy's experiments on reducing alumina; He reduces it in the electric
arc in presence of iron; He suggests a name for the metal ... 5
Prof. Benjamin Silliman's experiment with Dr. Hare's blow-pipe; Oer-
sted's attempt to reduce aluminium chloride; Berzelius' attempt to
reduce cryolite 6
Professor Frederick Wohler, of Gottingen, isolates aluminium as a
metallic powder, in 1827 7
Wohler obtains the metal in globules, in 1845; Professor Henri Saint-
Claire Deville obtains aluminium en masse, in 1854 . ... .8
Deville's first attempts; His paper read before the French Academy on
February 6, 1854 . . 9
The Academy aids Deville in his further work ; A reclamation by
Chenot; Further experiments at the Ec61e Normale; Reduction of
aluminium chloride by the battery 10
Deville's experiments in manufacturing sodium; Installation of the
sodium process at Rousseau Bros, chemical works at La Glaci^re;
Deville and Bunsen publish their electrolytic methods; The Emperor
Napoleon III. becomes interested and defrays the expense of further
experiments H
(XV)
xvi CONTENTS.
PAGE
TheTissier Bros, experiment on producing sodium; Deville's work at
Javel; The industry on a firm basis ' ^^
Exhibit of aluminium at the Paris Exposition, 1855; Misunderstanding
between Deville and the Tissier Bros 13
Tissier Bros, start an aluminium works near Rouen; History of this
14.
enterprise ^^
Deville and his friends put up a large plant at La Glaci&re; Removal to
Nanterre; Removal to Pechiney and Co.'s works at Salindres; Tissier
Bros, publish their "Recherchessurl'Aluminium" {1858) . . 15
Deville publishes his "De I'Aluminium" (1859); Hi^ conclusions as to
the usefulness of aluminium 16
Experiments of Dr. Percy and H. Rose on reducing cryolite; Manufac-
ture of aluminium by A. Monnier, of Camden, N. J.; Calculation of
cost of the new metal by W. J. Taylor 17
The first aluminium works in England, at Battersea (1858); Bell Bros,
works near Newcastle-on-Tyne; Project to start works at Berlin; Dr.
Clemens Winckler's retrospect, 1879 18
Condition of the aluminium industry in 1879 19
The industry from 1879 to 1882; W. Weldon's views on its prospects in
1883 . 20
The search for a substitute for sodium ; Webster's improvements in the
industry .21
H. Y. Castner's invention for producing sodium; His experiments in
New York 22
Castner's demonstration in England; Unites with Webster to form the
"Aluminium Company, Limited; " Large works at Oldbury near Bir-
mingham, stop making aluminium in 1891 ...... 28
Revival of electric methods, using dynamos instead of the battery;
Gratzel's process 24
Kleiner's process; Hall's process, invented in 1886, essentially different
in principle from previous attempts 25
Incorporation of the Pittsburgh Reduction Co. to work Hall's process;
Works at Kensington, Pa., and Niagara Falls; Minet's experiments
at Creil and works at Saint Michel, Savoy 26
The electric-furnace methods; Siemens furnace; Grabau's experiments;
Mierzinski's remarks 27
Cowles Bros, process, 1885; Plant at Lockport, N. Y., and works in
England; The principle of the process . 28
H^roult's processes; Principle of his alloy process 29
The "Aluminium Industrie Actien Gesellschaft " formed to work
HSroult's processes; Dr. Kiliani, manager of their works at the Falls
of the Rhine; The Hiroult process in France 30
Experiments with H^roult's process in the United States; The "Alliance
Aluminium Co., of London," formed to work Netto's sodium process. 31
Failure of the Alliance Aluminium Co.; Grabau's improvements in pro-
CONTENTS. xvii
PAGE
ducing sodium and aluminium fluoride; Colonel Frishmuth's works
in Philadelphia 32
Exhibit of aluminium at the Paris Exposition, 1889; Progress of the in-
dustry since 1890 33
The Cowles Electric Smelting Co. sued for infringement of the Hall
process; Exhibits of aluminium at the Columbian Exposition in Chi-
cago, 1893; The production of aluminium one of the great achieve-
ments of the century 34
Statistics; The decline in the price of aluminium and aluminium bronze. 35
Production of aluminium in France from 1854 to 1892; Production in
England; In Switzerland 36
Production of the United States from 1883 to 1894; Total aluminium
produced in the world to the end of 1892; World's production in 1893;
An estimate of the production in 1894 37
The probable production in 1895 38
CHAPTER II.
Occurrence of Aluminium in Nature.
Clarke's estimate of the proportion of aluminium in the earth's crust;
Not found metallic; Most frequent combinations in rocks, soils and
clays; Occurrence in some plants; Ricciardi's experiments on the
assimilation of alumina by plants 39
Composition of the most frequent aluminium minerals; Bauxite the
most useful mineral for the aluminium industry 40
Localities in which bauxite occurs ; Deposits worked in the United
States; Value per ton 41
Analyses of foreign bauxites 42
Analyses of American bauxites 43
Laur's generalizations concerning French bauxites . . . .44
Hunt's generalizations on American bauxites; The occurrence of cryo-
lite in Greenland 45
Composition of cryolite; Amount imported into the United States; De-
scription of a small deposit in Colorado 46
Analysis of the Colorado cryolite; The sources of corundum . . 47
Mining of corundum in the United States; The composition and proper-
ties of kaolin 48
Localities of the large kaolin beds; Value of kaolin as an aluminium
ore; Common clays 49
Native sulphate of alumina; Deposits in New Mexico, Colorado and
Ohio 50
Economic value of the aluminium sulphate deposits . . . .51
xvni CONTENTS.
CHAPTER III.
Physicai, Properties of Ai,uminium.
PAGE
Commercial aluminium not chemically pure; The most frequent im-
purities 52
The influence of small amounts of impurities on the physical properties
of the metal 53
Analyses of commercial aluminium ; Notes on the analyses . . .54
Recent analyses of present commercial metal 55
Difference in the composition of metal made by the sodium and the
electrolytic methods; The different conditions in which silicon exists
in aluminium; Rammelsberg's analyses ...... 56
Absorption of gases by molten aluminium; Dumas' analyses; Author's
observations; Tie Verrier's detection of carbon in commercial alumin-
ium . ..... 57
Influence of carbon on the physical properties of aluminium; Le Ver-
rier detects nitrogen in commercial aluminium ... .58
Influence of nitrogen on the physical properties of aluminium; The
color of pure and impure aluminium ....... 59
Tarnishing of aluminium in the air; Fracture of purest aluminium . 60
Fracture of impure ahiminium; Hardness; Testing quality -with the
knife; Hardening by cold working .61
Comparison of the hardness of aluminium with other metals; Specific
gravity . 62
Influence of impurities on the specific gravity; Increase of specific
gravity by working . . ....... 63
Comparison of the specific gravity of aluminium and other metals . 64
Comparative value of equal weights and equal volumes of the different
metals; Fusibility 65
Melting point determined by the electric pyrometer; Influence of im-
purities on the melting point; Volatilization; Odor .... 66
Taste; Magnetism; Sonorousness 67
Sound produced by an aluminium bell, bar and tuning-fork; Alumin-
ium sounding boards 68
Velocity of sound in aluminium; Crystalline form; Elasticity . . 69
Tensile and compressive strength ........ 70
Table of tensile tests . . 71
Table of compressive tests; Transverse tests . . . . 72
General conclusions of Messrs. Hunt, Langley and Hall; Variation of
tensile strength with the temperature 73
Influence of working and annealing on the mechanical properties;
Tensile strength in comparison with weight 74
Comparison of the tensile strength with that of other metals, section
for section and weight for weight; Malleability . ... 75
CONTENTS. XIX
PASE
Thickness of aluminium leaf; Color by transmitted light; Ductility . 76
Expansion by heat; Specific heat 77
Determinations of the specific heat by Regnault, Kopp, Mallet, Tom-
linson, Naccari, Le Verrier 78
Specific heat and latent heat of fusion as determined by Pionchon and
the author 79
The amount of heat in molten aluminium; Agreement with Dulong
and Petit's law 80
Slow melting of aluminium due to its great latent heat of fusion; Com-
parison with other metals; Electric conductivity ..... 81
Professor Dewar's determinations of the electric conductivity at very
low temperatures; Conductivity for heat ...... 82
CHAPTER IV.
Chemical Properties of Aluminium.
Atomic weight; Action of air . . . . , . . . .83
Resistance to air when melted; Action of air and water together;
Piqures 84
Combustion of aluminium powder or leaf ; Action of water . . .85
Decomposition of water by aluminium leaf; Action of hydrogen sul-
phide and sulphur 86
Experiment of the author with hydrogen sulphide and molten alu-
minium . 87
Action of sulphuric acid; Ditte's explanations 88
Le Roy's quantitative tests with sulphuric acid 89
Action of nitric acid; Ditte's observations 90
Experiments of Le Roy, Lunge and the author on the action of nitric
acid; Use of aluminium in the Grove battery; Action of hydrochloric
acid ... .91
Action of hydrobromic, hydriodic and hydrofluoric acids; Experiment
by the author; Action of organic acids, vinegar, etc 92
Action of the acids found in food; Deville's prediction of the usefulness
of aluminium for culinary utensils; Lubbert and Roscher's experi-
ments with thin foil 93
Balland's exhaustive tests with foods ; Rupp's results; Lunge and
Schmid's experiments 94
Details of Lunge and Schmid's tests 95
Conclusions from these tests; Confirmation of these results by actual
experience of two years with aluminium culinary utensils . . -96
Action of common salt, molten and in solution; Sea- water; Aluminium
boats ■ ^'^
CONTENTS.
PAGE
Action of organic secretions, the saliva, etc 98
Action of caustic potash, caustic soda; Quantitative tests . . .99
Action of ammonia; Lime water; Solutions of metallic salts . . . 100
Action of solutions of mercury, copper, silver, lead .... 101
Action of solutions of zinc, alkaline chlorides, aluminium salts; Action
of melted fluorspar; Use as a flux 102
Use of cryolite as a flux; Action of molten silicates and borates . . 103
Action of fused nitre; Purification of impure aluminium by nitre; Re-
action with alkaline sulphates and carbonates 104
Reaction of aluminium on oxides of manganese, zinc, iron, lead, copper,
barium 105
Greene and Wahl's process of producing pure manganese; Action of
phosphate of lime, silver chloride, mercurous chloride, carbonic oxide,
hydrogen, chlorine, bromine, iodine, fluorine 106
CHAPTER V.
Properties and Preparation of Aluminium Compounds.
General considerations; Position of aluminium in the periodic classifi-
cation of the elements . 107
Observations on the structure of aluminium compounds . . . 108
The tri-valency of aluminium ; Aluminates ...... 109
Neutral salts of aluminium; Basic salts; General methods of formation
of aluminium salts ... 110
General properties of aluminium salts; Chemical reactions in solution;
Reactions before the blowpipe Ill
Alumiuium oxide; Physical and chemical properties . . . .112
Hydrous aluminium oxides, natural and artificial; The soluble hydrate. 113
Aluminates; Potassium aluminate; Sodium aluminates; Barium alumi-
nate ...... 114
Aluminates of calcium, zinc, copper, magnesium, iron, beryllium; Alu-
minium chloride 115
Hydrous aluminium chloride; aluminium-sodium chloride . . .116
Double chlorides of aluminium with phosphorus, sulphur, selenium,
ammonium 117
Aluminium-chlor-sulphydride ; Aluminium-chlor-phosphydride ; Alu-
minium bromide; Aluminium iodide 118
Aluminium fluoride; Methods of production 119
Fluorhydrate of aluminium; Aluminium-hydrogen fluoride; Alumin-
ium-sodium fluoride .120
Aluminium sulphide; Double sulphides with sodium and potassium . 121
Use of aluminium sulphide in the laboratory for generating hydrogen
sulphide; Aluminium selenide; Aluminium borides . . . .122
CONTENTS. xxi
PAGE
Aluminium boro-carbides; Aluminium carbide 123
Production of aluminium carbide in the electric furnace by Le Verrier . 124
Composition and properties of aluminium carbide; Aluminium nitride 125
Aluminium sulphates, anhydrous and hydrous 126
Basic aluminium sulphates 127
Alums; Potash alum; Ammonia alum .... . . 128
Soda alum; Bouble sulphates of aluminium and the metals; Aluminium
selenites 129
Aluminium nitrate; Aluminium antimonate; Aluminium phosphates . 130
Aluminium carbonate; Aluminium borate 131
Hydrous aluminium borates; Aluminium silicates; Blast furnace slags 132
CHAPTER VI.
Preparation of Aluminium Compounds for Reduction.
The preparation of alumina; Preparation from alums or aluminium sul-
phate .... .133
Preparation of alumina from ammonia alum ...... 134
Method used by Deville at Javel; Tilghman's method . . . 135
Webster's process of making alumina from potash alum . . 136
Preparation of alumina from bauxite ; Method uSed at Salindres . . 137
Heating with soda and washing out the aluminate ... . 138
Apparatus used for washing; Precipitation of alumina by carbonic acid
gas 139
Apparatus used for the precipitation ; The barattes . . . 140
Washing and drying the precipitated alumina; Behnke's method of
treating bauxite; Lieberfs method 141
Muller's method for extracting alumina from silicates; Use of common
salt to decompose bauxite; Wagner's method of treating bauxite . 142
Laur's method of using sodium sulphate to decompose bauxite; Lowig's
experiments on precipitating alumina from sodium aluminate solu-
tion; Dr. Bayer's improvements . 143
Preparation of alumina from cryolite; The dry way .... 144
Furnace for heating cryolite with chalk; Thomson's method . . 145
Conduct of the operation ; Washing the fusion .... 146
Production of the carbonic acid gas for precipitation .... 147
Composition of the precipitate; Action of steam on molten cryolite;
Utilization of aluminous fluoride slags 148
Utilization of the residual slags from sodium retorts by fusing with the
aluminous slags; Decomposition of cryolite in the wet way . . 149
Method used by Deville at Javel; Modification of this process by Sauer-
wein ............. 150
Reactions in Sauerwein's process; Weber's method of decomposing
cryolite; Schuch's reaction 151
xxii CONTENTS.
Preparation of aluminium chloride and aluminium-sodium chloride . 152
Method used by Beville on a small scale at Javel . . . 1 53
Manufacture by Deville on a large scale 154
Furnace used and working of the operation . . . 155
Output of the furnace; Purification of the crude chloride . . .156
Deville's idea of making the double chloride; Margottet's description
of the apparatus used at Salindres . ... 157
Conduct of the operation at Salindres . . . . . 158
Cost of making the double chloride at Salindres . . . 159
Plant of the Aluminium Company, Limited, at Oldbury, near Birming-
ham, England . . . . _. . . 160
Arrangements of the furnaces and conduct of the operation . . .161
Output of this plant; Purity of the double chloride . .162
Castner's method of purifying the double chloride . ... 163
Cost of the purified double chloride; Gadsden's method of producing
aluminium chloride; Count R. de Montgelas' improvement . . 164
Prof. Mabery's process for producing aluminium chloride in the electric
furnace; Curie's method; Warren's general process for anhydrous
metallic chlorides . . ... 165
Camille A. Paure's process; Description by Berthelot . 166
Details of Faure's process; Output claimed; DuUo's method of making
aluminium chloride from clay ... ... 167
Remarks on Dullo's suggestions; The preparation of aluminium fluoride
and artificial cryolite . ....... 168
Berzelius' method of making artificial cryolite; Deville's methods . 169
Pieper's reactions in the wet way; Bruner, Deville and Hautefeuille on
making aluminium fluoride . . . . 170
Grabau's processes; Aluminium fluoride from aluminium sulphate and
fluorspar . . ... ... 171
Aluminium fluoride indirectly and directly from kaolin . . . 172
Precautions necessary to obtain it free from iron 173
The preparation of aluminium sulphide; Fremy's researches . . . 174
Purity of the aluminium sulphide produced .... . 175
Reichel's results; Experiments of the author . .... 176
Propositions of Comenge, Petitjean, etc. . . • 177
Lauterborn's patent anticipated . .... 178
CHAPTER VII.
The Manufacture of Sodium.
Relations of the production of sodium to the aluminium industry; Isola-
tion of sodium by Davy, Gay Lussac and Thenard, Curaudau . . 179
Briinner's apparatus; Donny and Mareska's condenser; Deville's im-
provements at Javel (1855) . ]80
183
184
185
186
187
188
189
190
191
CONTENTS. xxiii
PAGE
The chemical and physical properties of sodium . ... 181
Method of reduction used at Javel; Composition of the mixtures for re-
duction .... .... ... 182
Utility of the different ingredients of the mixtures; Difficulties of con
densing sodium vapor . .
Mixture used at La Glacifere and Nanterre; Charging the apparatus
Description of retorts and condensers ; Manufacture in mercury
bottles ... . .
The furnace used for manufacture in mercury bottles
Detailed description of condensers
Conduct of the operation . . ...
Handling of the condensed sodium; The temperature necessary for re
ductiou ... ....
Use of decarburized, cast-iron bottles; The continuous manufacture in
cylinders
Furnace for manufacture in cylinders
Arrangement of the cylinders in the furnace 192
Charging and discharging the cylinders . .... 193
Tissier Bros. ' method of procedure at Rouen 194
Furnace used by Tissier Bros ... 195
Charging and discharging Tissier's furnace 196
Causes of loss of sodium; Deville's improvements at La GlaciSre (1857) 197
Deville's large cylinder furnace; Difficulties in its operation . . 198
Deville's attempts to use cast-iron retorts; Deville's improvements at
Nanterre (1859) ... . . ... 199
Necessity of protecting the iron cylinders; Deville returns to smaller
apparatus ... . 200
Cost of sodium at Salindres in 1872; An experiment of Deville's in 1864;
Wagner's method of preserving sodium .... . 201
Reduction of potassium and sodium compounds together; Thompson
and White's method . ... ... 202
Blackmore's process of reducing carbonate of soda; Thowless' ap-
paratus; Jarvis' device for using fire-clay apparatus; Castner's process 203
History and principle of Castner's invention 204
Reaction on which the process is based; Form of furnace used . 206
Experimental furnace erected in England
Conduct of the operation in this furnace .
Yield of the furnace; Composition of the residues .
Cost of sodium by the Castner process
Erection of large works to operate the Castner process
Description of the largest furnaces ....
Manner of working and output of these furnaces
Preservation of the sodium; Reactions in the process
Netto's sodium process; The Alliance Aluminium Company
Details of Netto's apparatus
207
208
210
211
212
213
214
215
217
218
xxiv CONTENTS.
PAGE
Reduction of sodium compounds b3' electricity; Jablochaff's apparatus;
Roger's method 219
Details of Roger's experiments ... 220
Grabau's observations on the electrolysis of molten sodium chloride . 222
Details of Grabau's electrolytic process; Castner's process of electrolyz-
ing caustic soda .... 223
CHAPTER VIII.
Thb Reduction of Aluminium Compounds from the Standpoint of
Thermai, Chemistry.
The proper way to use the data of thermo-chemistry .... 226
Critical temperatures below which reactions do not occur . . . 227
Influence of physical state in determining a reaction; The heat of forma-
tion of some aluminium compounds ...... 228
The heat of formation of alumina compared with that of other oxides;
Elements which reduce alumina easily ..... 229
Possibilities of the reduction of alumina ....... 230
Reduction of alumina by carbon; Necessary conditions to be fulfilled . 231
Heats of formation of chloride, bromide and iodide of aluminium, and
other metals 232
Deductions as to the agents capable of reducing these aluminium salts 233
Heat of formation of aluminium fluoride and other metallic fluorides . 234
Observations on the reduction of aluminium fluoride; Heat of formation
of aluminium sulphide and other metallic sulphides . . . 235
Observations on the reduction of aluminium sulphide; Electricity as a
reducing agent ... 236
The voltage necessary to produce decomposition of metallic fluorides,
chlorides, oxides and sulphides; Tabular view of these data; Observa-
tions thereon ... ...... 237
Electrolysis of baths containing several ingredients; Illustration from
Hall's process ... . 938
Illustration from Minet's process; The voltage required to decompose
alumina at different temperatures . 239
Calculation of the temperature at which hydrogen can begin to reduce
alumina; The same calculation for carbon . . . 240
Alumina has been reduced by carbon in an iron blast furnace; Peculiar-
ity of acetylene gas as a reducing agent . . ... 241
Thermal aspect of other reactions used in the aluminium industry; The
production of aluminium chloride from alumina ..... 242
The production of aluminium sulphide from alumina; Peculiarity of
carbon bi-sulphide from a thermal standpoint • . . . . 244
CONTENTS.
CHAPTER IX.
Reduction op Aluminium Compounds by Means of Potassium or
Sodium.
PAGE
Classification of methods ; The reduction of chlorine compounds ;
Oersted's experiments (1824) 246
Wohler's experiments (1827); Wohler was repeating Oersted's work. 247
Wohler isolates aluminium as a metallic powder ; His experiments
in 1845 . 248
Globules of aluminium obtained by Wohler in 1845 . . . 249
Impurity of Wohler's metal; Deville's experiments in 1854 . 250
Deville obtains pure aluminium in ingots ...... 251
Deville's methods devised in his laboratory and applied at Javel (1855). 252
Details of the apparatus employed; Conduct of the operation 253
Deville's dissatisfaction with this apparatus and its results . . 255
Deville reduces aluminium chloride by sodium vapor . . . 256
Deville's perfected process as used at Nanterre (1859) ■ • • ^^'^
Details of Deville's improvements . . 258
Reduction in crucibles; Lining of crucibles ...... 259
Reduction on the bed of a reverberatory furnace . ... 261
Deville's views on the aluminium industry in 1859 . . 263
The Deville process as operated at Salindres in 1882 . . . 264
The chemical reactions in the process ... . 265
Description of furnace used and mode of operation . . . 266
Cost of aluminium at Salindres; Niewerth's process . . 268
Gadsden's sodium vapor process; Frishmuth's claims . . . 269
H. von Groussillier's improvement; The Deville-Castner process . 270
Description of Castner's works; Conduct of the operations . . . 271
Efficiency of the process; Closing of these works ... . 273
CHAPTER X.
REDUCTION OF Aluminium Compounds by Means of Potassium or
Sodium {Continued).
Methods based on the reduction of cryolite; Experiments of H. Rose
(1855) .... 274
Experiments of Percy and Dick (1855)
Deville's methods (1856-8) . . .
Tissier Bros', methods; Impurity of the metal
Wohler's improvements on Tissier's method; Gerhard's furnace
Thompson and White's patent; Hampe's experiment; Netto's experi-
ments at Krupp's works at Essen ... .... 290
288
285
287
289
XXVI CONTENTS.
PAGE
Formation of the Alliance Aluminium Co. to work Netto's process . 291
Description of Netto's processes as actually carried out .... 292
Return from Netto's process; The apparatus used at Essen . . 293
Netto's other devices; Failure of the Alliance Aluminium Co. ; Grabau's
process (1887) 294
Advantages of Grabau's method of reducing aluminium fluoride . 295
Reactions in Grabau's process; Description of the operation . . 296
Description of the furnace and apparatus used ..... 297
Great purity of the aluminium produced by Grabau .... 299
CHAPTER XI.
Reduction of Aluminium Compounds by the Use of Ei<ectricity.
Preliminary observations on the laws of electrolysis . . . 301
Calculation of the voltage necessary to decompose aluminium com-
pounds . . . . . . . . 302
Utilization of such calculations; Electrolysis of aqueous solutions 303
Electrolysis using a soluble anode .... ... 304
Electrolysis using insoluble anodes . 305
Electrolysis of baths containing several compounds .... 306
Deposition of aluminium from aqueous solution; Thomas and Tilly's
patent . . 307
Corbelli's process; Thompson's claims; Gore's experiments . . . 308
Dr. Gore's error; Jeangon's process 309
Successful plating by the Harvey Filley Plating Co., of Philadelphia;
Bertrand's assertion; Braun's methods ....... 310
Dr. Fischer's experience with Braun's method; Farmer's apparatus;
Senet's process ; Frishmuth's plating ; Overbeck and Niewerth's
patent . . ... .311
Reinbold's recipe; Count R. de Montgelas' patents . 312
A. Walker's methods of procedure . ... . . 313
Bull's proposition; Burghardt and Twining's patents .... 314
Patents of Gerhard and Smith; Taylor and Coulson; Experience of
Sprague, Dr. Winckler and Dr. Gore 3I5
Opinions of Dr. Mierzinski, Hampe and Watt; Experiments of Dr.
Lisle; Aluminium plating on the Philadelphia Public Buildings . 316
Aluminium plating by Mr. Darling at the Tacony Metal Co. 's works,
Philadelphia gjy
Non-aqueous electric processes; Difficulty of a satisfactory classification. 318
Davy's experiments (1810); Duvivier's experiment (1854) . . .319
Bunsen's and Deville's methods (1854) ... . . 320
Details of Deville's apparatus 32i
Details of Bunsen's apparatus . . .... 322
CONTENTS.
Deville and Caron's method of plating aluminium on copper . . 323
Deville's experiments not an anticipation of Hall's process; Le Chatel-
lier's patent . ... 324
Monckton's proposition; Gaudin's process; Kagensbusch's process . 325
Berthaut's proposition to use dynamos; Gratzel's process . . . 326
Apparatus used by Gratzel; Later modification of his process . . 327
Prof. Fischer's criticism of Gratzel's process; Operation of the process
at Bremen . . .... .... 328
Abandonment of the Gratzel process; Cowles Bros.' process . . . 329
Professor Mabery's description of the Cowles electric furnace . . 330
Dr. T. Sterry Hunt's remarks ... 331
Bradley and Crocker's form of retort used by the Cowles Co. . . 382
A. H. Cowles' form of furnace for continuous working; W. P. Thomp-
son's paper on the Cowles process, read in England .... 333
Cowles Bros', plant at Lockport, N. Y.; Details of the furnaces . . 334
Charging the furnaces . 335
Details of the operation of Cowles' furnaces 336
The enlarged plant at Lockport . 339
The Cowles Syndicate Co.'s works at Stoke-on-Trent, England . . 340
Analyses of Cowles Bros', aluminium bronze 341
Analyses of ferro-aluminium and slags . 342
The reactions in Cowles Bros', process 343
Electrolysis necessarily a secondary factor in the operation of these
furnaces .... 344
H. T. Dagger's experiment with the alternating current in a Cowles'
furnace ....... .... 345
History of the suit — Pittsburgh Reduction Co. vs. Cowles Electric
Smelting and Aluminium Co. 346
Menges' patent; Farmer's process; Kleiner's process . . 347
Kleiner's experiments at Schafthauseu ; Experimental plant in
England 348
Dr. Gore's report on Kleiner's process 349
Output of aluminium by this process; Purity of the metal . . . 352
Kleiner's process outclassed by later processes; Lossier's proposition to
decompose natural silicates of aluminium
Omholt's furnace; Minet's process .
Apparatus used in Minet's process .
Composition and properties of the baths .
Minet's views on the reactions in his baths
Electrical measurements on Minet's pots
Separation of iron and silicon by a carefully regulated current . . 360
Output and quality of aluminium; Installations of this process . . 361
Minet's plant now working on the Hall process; Feldman's process . 362
Uselessness of Feldman's methods; Warren's experiments . . .363
Zdziarski's patent; Grabau's apparatus 364
353
364
355
357
358
359
xxviii CONTENTS.
PAGE
Roger's process; Details of experiments ....... 365
Dr. Hampe on the electrolysis of cryolite . . ... 368
History of Hall's experiments; Interference with H^roult in the United
States patent ofi&ce . ... .... 373
Specifications and claims of Hall's patents 374
Installation of Hall's process at Pittsburgh 376
Conduct of the operation in Hall's pots 377
Consumption of carbon anodes 378
Alumina used in the process; Efficiency of the electrolysis . . . 379
Estimate of cost of aluminium by the Hall process in 1889; Enlarge-
ment of the plant in 1890 381
Removal and enlargement of the plant in 1891 ; The Niagara Falls
plant 382
Total output of the Pittsburgh Reduction Co.'s works; Efficiency of
the process . 383
Chemical reactions in Hall's baths; Alumina is the compound primarily
decomposed ... ...... . 384
Theory of an aluminium oxy-fluoride not proven; Hdroult's processes. 386
Similarity of Hferoult's first process to that of Hall .... 387
HSroult's alloy process; Installation at the Falls of the Rhine . . 388
Description of furnaces used . ....... 389
Conduct of the operation ... 390
Output at full efficiency; Theoretical output ..... 392
H^roult's alloy process not essentially electrolytic in its operation . 393
HSroult's apparatus for pure aluminium .... 394
Recent enlargements at the Rhine Falls ; The Heroult process in
France 395
Hdroult's alloy process at Boonton, N. J 896
Details of cost of pure aluminium atNeuhausen; Faure's electrolytic
process ... 398
Winkler's patent; Willson's crucible 399
Grabau's electrolytic process; Bucherer's patent ..... 400
The Neuhausen sulphide process . 401
CHAPTER XII.
REDUCTION OF Al<UMINIDM COMPOUNDS BY OTHER MEANS THAN SODIUM
OR El,ECTRICITY.
Reduction by carbon without the preseuce of other metals; Chapelle's
attempt ... 402
Reinar's experiment with alum; Thowless' claim . ... 403
Patent of Pearson, Liddon and Pratt; Bessemer's ideas .... 404
Reduction by carbon and carbon dioxide; Morris's claims . . . 405
CONTENTS. xxix
PAGE
Ideas of P. A. Emanuel; Reduction by hydrogen 406
Gerhard's #patent; Success of H. Warren in reducing alumina by
hydrogen 407
Reduction by carburetted hydrogen; Fleury's experiments; Petitjean's
statement 408
Experiments of L^b^deef, Dr. Lisle, R. E. Green 409
Reduction by cyanogen; Knowles' patent; Corbelli's process; Experi-
ments of Deville and Lowthian Bell 410
Reduction by double reaction; Comenge's process; Niewerth's furnace 411
Process of G. A. Faure; Reduction by or in presence of copper; Calvert
and Johnson's experiments ........ 413
Evrard's method of making aluminium bronze; Benzon's patent . 414
Faure's patent .... 415
Experiments by BoUey, List, Dr. Lisle and Hampe . . .416
Experiments of Reichel and the author; Processes of A. Mann and L. Q.
Brin ... . . .... 417
Reduction by or in presence of iron; Experiments of Comenge, Lauter-
born, Reichel and the author; Niewerth's process .... 418
Thompson's method 419
Calvert and Johnson's experiments 420
Chenot's reclamation; Use of spongy iron . . . . 421
Faraday and Stodart's investigations; Wootz steel 422
Presence of aluminium in pig-iron ; Reports by various analysts . . 423
Billings' attempt to reduce alumina in contact with iron; Cleaver's
patent . . ... . . 424
Ostberg's statement about aluminium in pig-iron; Brin Bros.' process . 425
Baldwin's process for treating foundry iron . . . . 426
Alloy of the Williams Aluminium Company; Bamberg's method . . 427
Aluminium in pig-iron from Marshall Bros.' Newport furnace . , 428
Reduction by or in presence of zinc; Statements of Bdk^toff, DuUo,
Basset . ... 429
Wedding's remarks on Basset's process; Experiment by the author . 431
Works of F. J. Seymour at Findlay, Ohio ... . . 432
Lauterborn's method of reduction by zinc . .... 433
Clark's doubtful processes .... ... 434
Dr. Lisle on reducing aluminium sulphide by zinc; Bamberg's patent;
Reduction by lead ... 435
Reduction by manganese; Weldon's claim; Greene and Wahl's observa-
tions t 436
Reduction by magnesium; Gratzel's patent; Roussin's statement; Mont-
gelas' patent; Winkler's experiments on alumina . . . 437
Reduction by antimony; Lauterborn's formulas; Experiment by the
author 438
Reduction by tin; Process of Howard and Hill; Dr. Lisle's successful
experiments . 439
CONTENTS.
PAGE
Reduction by phosphorus; Grabau's process . . ... 440
Reduction by silicon; Wanner's claims «• -441
CHAPTER XIII.
Working in AItItminium.
Melting; Deville's recommendations 442
Biederman's directions; The author's methods . ... 443
Bauxite and magnesite linings for crucibles and furnaces . . 444
Casting; Deville's remarks 445
Casting under pressure . ..... . 446
Aluminium hollow- ware casting; Purification of aluminium; Freeing
from slag . . 447
Freeing from dissolved impurities 449
Removal of zinc by distillation; Test of Buchner's method of purifica-
tion by hydrogen gas . . 450
Purification by other gaseous reagents; Mallet's method of making
chemically pure aluminium 451
Ive Verrier's experiment with alkaline fluoride; Use of sodium to re-
move dissolved gases; Annealing; Hardening 452
Effect of chilling; Rolling; Beating into leaf 453
Rolling into tubes by the Mannesmann process; Very fine tubes made
by Ivins, of Philadelphia; Drawing into wire . . . 454
Stamping and spinning; Grinding, polishing and burnishing . . 455
Special polishes for aluminium; Engraving; Cleaning and pickling;
Mat . . ... 456
Welding by electricity; Soldering; Requirements of a satisfactory
solder; Difficulties peculiar to aluminium . . . . 457
Deville's views on soldering aluminium . . . 458
Mourey's first practical solders . ... ... 459
Bell Bros. ' method of using Mourey's solders ..... 461
Frishmuth's solders; Schlosser's solder for dental work .... 462
Bourbouze's solder of aluminium and tin; Thowless' patent solder . 463
Patents of Sellon and Sauer; Novel's alloys for soldering . . . 464
Land's mechanical method; Aluminium specially prepared for soldering 465
Special fluxes recommended; Roman's solder . . . 466
The "Alsite" solder; The phosphorized solder of Mr. Joseph Richards,
of Philadelphia 467
Success of Richards' phosphorized solder; Methods of using . . . 468
Coating other metals with aluminium; Veneering as practiced by M.
Sevrard . . 469
Dr. Winckler's experience . 470
CONTENTS. xxxi
PAGE
Dr. Gehring's method of aluminizing; Broadwell's process for coating
sheet-iron ...... 471
Plating other metals on aluminium; Gilding and silvering by Mourey
and others 472
Veneering with silver or platinum; Rolling together aluminium and
copper sheet; Wegner and Guhr's methods for electro-plating and
coloring; Neeson's methods; The uses of aluminium . . . .473
The place of aluminium among the useful metals . ... 474
The first articles made of aluminium; Use in the French army . . 475
Recommendations of the German military commission; Use for boats . 476
The yacht " Vendenesse;" The French aluminium torpedo boat . . 477
Explorer Wellman's boats and sledges; The yacht "Defender;" Use for
vehicles and flying machines 478
Use architecturally and for decorations; Suitability for mine cages 479
Use in surgery; Dental plates ... . . . 480
Use for scientific instruments; Captain Gordon's sextant . . .481
Advantages of aluminium for engineering and electrical instruments;
Chemical and bullion balances . . 482
Troemner's assay balances; Use for aluminium for minor coinage . . 483
Advantages and suitability for coinage; Use for chemical apparatus . 484
Use for culinary utensils; Its well-established advantages
Use for table ware; Disadvantages for some articles
Aluminium constructions; Use in the battery
Substitution for lithographic stone; Strecker's directions
Use for flash-light powder; Recipes of Villon and Black
Miscellaneous uses ........
485
486
487
488
489
490
CHAPTER XIV-
Ai,i,OYS OF Aluminium.
General remarks; Methods of making the alloys . . . . 492
Division of the alloys into two classes; Influence of Aluminium on the
color of other metals ... 493
Contraction in alloying; Influence of aluminium on the specific gravity
of other metals . 494
Alloys with copper and iron to be considered separately; Alloys with
antimony 495
Unusual property of one antimony alloy; Roche's unstable alloy . . 496
Aluminium and arsenic; Aluminium and bismuth; Aluminium and
boron . . 497
Aluminium and cadmium; Aluminium and calcium .... 498
Aluminium and chromium; Langley's alloy 499
Aluminium and cobalt; Lejeal's test; Aluminium and gallium . . 500
xxxii CONTENTS.
PAGE
Aluminium and gold; Roberts-Austin's tests; Niirnberg gold; Andrews'
experiments .... ....••• 501
Peculiar properties of the violet alloy discovered by Roberts-Austin . 502
Aluminium and lead; Cupellatiou of aluminium 503
Aluminium in anti-friction and type metal; Aluminium and magnesium. 504
Aluminium and manganese; Cowles' alloy • 505
Aluminium and mercury; Deville's mistake; Simple experiment by the
author; Cailletet's method of amalgamation ..... 506
Joule's electrical experiment; Gmelin's observation; Method of amal-
gamation by Watts; Bailie and Fury's study of the subject . 507
Composition and properties of a definite aluminium amalgam . . 508
Action of air, water, acids and other metals, on aluminium amalgam;
Aluminium and molybdenum ........ 509
Aluminium and nickel; Tissier's tests . ..... 510
I^ejeal's alloy with nickel ; The Pittsburgh Reduction Co.'s alloy;
Aluminium- nickel-copper alloys 511
Alloys of Sauvage, Baudrin, Webster; "Neogen" . . . 512
Webster's patented alloys ... ...... 513
" Lechesue; " Method of production and properties . . 515
Cowles Bros.' "Aluminium Silver" and "Hercules Metal;" Andrew's
alloys; Aluminium and phosphorus ... . . 516
Aluminium and platinum; Aluminium and silicon ; Alloys formed
while melting aluminium in crucibles ...... 517
Influence of silicon on commercial aluminium . . . . 518
Aluminium and selenium; Aluminium and silver ..... 519
Silver alloy for dental plates; " Tiers Argent " 520
Aluminium and sodium; Aluminium and tellurium .... 521
Aluminium and tin; Bourbouze alloy . 522
Decomposition of some aluminium-tin alloys 523
Aluminium deleterious to tin-foil; Heycock and Neville, and Minet, on
the fusing points of aluminium-tin alloys ...... 524
Aluminium and titanium; Wohler's alloy ...... 525
Levy's alloy; Alloy made by the Pittsburgh Reduction Company . . 526
Le Verrier's tests of titanium alloys; Aluminium and tungsten; Tests
by he Verrier .... . ,527
Aluminium and zinc; How zinc crept into some early commercial
aluminium .... . ... . 528
Aluminium hardened by zinc and copper; Use of aluminium in the
galvanizing bath and in Parke's desilverizing process .... 529
Aluminium-zinc-copper alloys; Aluminium brasses 530
Baur and Farmer's aluminium brasses; Tests of Cowles Bros', brasses. 531
Professor Tetmayer's tests of aluminium brasses 532
Richards' bronze .... 533
CONTENTS.
CHAPTER XV.
Ai,uminium-Coppe;r Ai<i,oys.
PAGE
Division into two classes; General properties 534
Melting points; Indications of chemical alloys 535
Alloys containing small amounts of copper . ... 536
Aluminium hardened by copper; Tests of these alloys by Captain
Julien ... 537
Aluminium hardened by German silver; Alloys containing small
amounts of aluminium; Aluminium bronzes ... . 538
History of the aluminium bronzes 539
Constitution of aluminium bronzes; Are they chemical combinations? 540
Morin's arguments to prove that the bronzes are chemical alloys . . 541
Action of small amounts of aluminium on bronze, brass and copper . 542
The reducing action of aluminium on dissolved oxides in molten
metals . 543
Bronzes made from alumina versus those made with metallic alu-
minium 544
Method of preparing the bronzes industrially . .... 545
Influence of impurities in the aluminium or copper on the properties
of the bronzes ...... .... 546
Re-melting the bronzes improves their quality ..... 547
Fluidity of the bronzes when melted; Casting the bronzes . . . 548
Thomas D. West on " Casting Aluminium Bronze " . . 549
Shrinkage of the bronzes in cooling; Color . . £52
Specific gravity of the bronzes; Hardness .... . 553
Transverse and compressive strength ... . 554
Tensile strength; Lechatelier's tests . . . . . 555
Tests of tensile strength by Deville, Strange, at the Watertown Arsenal
and Washington Navy Yard ......... 556
Details of tests of Cowles Bros', bronzes . 557
Diagram showing comparison of the strength of wrought-iron, tool-
steel, and two aluminium bronzes ........ 558
Professor Tetmayer's tests of the strength of the bronzes . . . 559
Diagram showing the variation of strength and ductility of the bronzes
with increasing proportions of aluminium; Le Chatelier's test of the
strength at various temperatures 560
Annealing and hardening the bronzes; Forging, hammering and
rolling -561
Filing, chipping and planing the bronzes 562
Anti-friction qualities of the bronzes 563
Conductivity for heat and electricity; Resistance to corrosion . . 564
Suitability of the bronzes for marine construction, chemical purposes
and statuary . 566
xxxiv CONTENTS.
PAGE
Various uses to which the bronzes are applied; Suitability for heavy
guns . ...
Suitability for propeller blades
Brazing and soldering the bronzes
Silicon-aluminium bronze .
Phosphor-aluminium bronze; Boron-aluminium bronze
567
. 568
. 569
. 570
. 571
CHAPTER XVI.
Aluminium-Iron Ahoys.
Iron in commercial aluminium . . ...... 672
Alloys made by Tissier Bros., Michel, and Calvert and Johnson . . 573
Ferro-aluminium ; Manufacture directly from alumina or from the
metals . . ... . . ■ 574
Aluminium in commercial steel, wrought-iron and pig-iron; Effect of
aluminium on the properties of steel ....... 575
Faraday's experiments with Wootz steel 576
Mitis castings; Use of aluminium in casting soft steel . . . 577
Experiments of Gilchrist and R. W. Bavenport .... 579
Spencer's experiments on casting steels . ..... 580
' ' Steel-aluminium ' ' for use in steel ; Effect of aluminium on wrought-
iron . ... 581
History of the Mitis process 582
Rise and progress of the Mitis process; Raw material used . . . 583
Composition of a melt of mitis metal ; Analyses of mitis castings . . 584
The process of making mitis castings ....... 585
Conduct of the process at the Chester Steel Casting Works . . . 586
Explanation of the action of aluminium in making mitis castings; Ost-
berg's views ..... ..... 587
R. W. Davenport's explanation inadequate . .... 588
The author's explanation of the increased fluidity of the melt . . 589
Why mitis castings are without blow-holes . .... 590
Discussion of Davenport's experiment and Howe's explanation . . 592
Professor Le Verrier's explanation ; Professor Arnold's experiment . 593
Summary of the author's views; Influence of aluminium in the puddling
furnace . . ... 594
Influence of aluminium on cast-iron . ...... 595
Systematic investigation of this subject by Messrs. Keep, Maybery and
Vorce . . .... .... 596
General outline of Keep's tests 597
Effect of aluminium on the solidity of the castings; Does the aluminium
remain in the iron ? 59g
Effect of aluminium on the transverse strength of castings . . . 599
Effect on the elasticity of the castings 600
CONTENTS. XXXV
PAGE
Effect on the grain of the castings 601
General effect of aluminium on the fluidity of cast-iron; Shrinkage . 602
Effect on the hardness of the castings . ... . 603
Practical advantages in pouring the castings; General testimony of ex-
perienced foundrymen . . . .... 604
Rationale of the action of aluminium on cast-iron ... . 605
CHAPTER XVII.
Analysis of Ai,uminium and Aluminium Alloys.
Ingredients to be determined; Qualitative tests to precede the quantita-
tive analysis ... 606
Qualitative blow-pipe tests; The specific gravity as an indication of
purity . ... .... 607
Schulze's test of the purity of commercial aluminium; Determination
of silicon . . . . .... 608
Separation of combined and graphitic silicon 609
Regelsberger's method for dissolving and estimating silicon . . 610
Determination of iron and aluminium .611
Separations of iron from aluminium 613
Determination of lead; Determination of copper; Determination of zinc 614
Determination of tin; Determination of silver; Determination of sodium 615
Determination of chlorine; Detemiination of carbon; Determination of
fluorine . . 616
Determination of titanium; Determination of chromium . . . 617
Analysis of ferro-aluminiums; Difficulty of estimating aluminium prop-
erly; Yates' method of procedure 618
Chancel's separation of iron from aluminium; Peter's modification of
Chancel's separation; Thompson's experience 619
Satisfactory separation of iron from aluminium by potassium cyanide;
Precipitation of iron by tri-methylamine 620
Blair's procedure for separating iron from aluminium . . . 621
Electrolytic separations of iron from aluminium; Classen's method;
Professor Smith's method ... . . . 622
Stead's method of separating iron from aluminium; Analysis of alu-
minium bronzes ... ..... 623
Determination of tin, lead and copper in the bronzes .... 624
Determination of iron, aluminium, zinc, cobalt and nickel . . . 625
Analysis of aluminium-zinc alloy; Analysis of aluminium-tin, alumin-
ium-silver, aluminium-nickel, aluminium-manganese and aluminium-
lead alloys ... 626
General remarks on the usefulness of making qualitative tests prepara-
tory to a quantitative analysis . 627
Index ... ... 629
ALUMINIUM,
CHAPTER I.
HISTORY OF ALUMINIUM.
Pliny* tells us that alumen was the name of several kinds of
salts used in dyeing, a white kind for dyeing bright colors and
a dark kind for dull colors ; that all alumen had an astringent
taste and was colored black by the juice of the pomegranate
(a reaction caused by iron). From all we can learn in the
writings of Pliny and Columella, it appears that the white
alumen must have been a mixture of aluminium sulphate with
more or less sulphate of iron. Why it was called alumen is
not certainly known, but it was probably derived from lumen,
light, in allusion to its brightening the colors when used in
dyeing.
About the eighth century a very pure alumen was made in
Rocca, near Smyrna, and hence called alumen Rocca, or in
modern times, rock alum. This was, indeed, a pure sulphate
of aluminium with sulphate of potash; in fact, our modern
alum, diflfering from the ancient alumen in that it contained
potassium, and was manufactured with care instead of being
merely a natural substance. The old name was, however, still
attached to the new product, and included in its scope the
vitriols, that is, the sulphates of iron and copper. Even in the
thirteenth century alum and vitriol vvere named together as re-
lated substances.
* Book 35, chapter 15.
(O
2 ALUMINIUM.
Paracelsus* in the sixteenth century first separated alum and
vitriols, on the ground that the base of the vitriols was metallic
and that of alum earthy.
Ettmiillerf discovered in 1684 that "alum is obtained by
acting on clay with sulphuric acid."
Stahl in 1702 expressed clearly his conviction that the un-
known base of alum was of the nature of lime or chalk, and for
fifty years thereafter this was the generally accepted idea.
Hoffman $ twenty years later announced that the base of
alum appeared to him to be a true, distinct earth. GeofiTroy,
in 1728, Hellot, in 1739, and Pott, in his famous Lithogeognosia,
in 1746, all reiterated this statement with increasing certainty,
until it was finally generally received as an accepted fact, and
the last named chemist gave it the name of thonichte erde, or
terre argilleuse.
In 1754 Marggraff,§ in three able dissertations on alum and
its earth, showed that this earth is certainly a distinct substance,
that it exists in all natural clays and can be extracted therefrom
by sulphuric acid, that the part of the clay not touched by the
acid is silica, and that, therefore, the purest white clay contains
only silica and the earthy base of alum. These memoirs settled
conclusively the composition of clay, and give rise to the term
argil or argil pier as the name of the earthy base of alum. It
was thus called until 1761, when Morveau,|| intent on revising
chemical nomenclature, decided that since alum was called sel
alumineux, the proper name for its base should be altimine,
thus avoiding all confusion with argille and terre argilleux, the
terms designating clay and clayey earth. In German, however,
the earth of alum is still called thonerde — clay earth ; in English,
the French alumine was adhered to until about 1820, when it
was anglicised into alumina.
* Book 3, p. 64.
t Chymia Rationalis ac Experimentalis.
X Observationem physico-chemicarum Selectiorium, 1722,
§ Opusc. Chim. de Marggraff, I, p. 8.
II Dictionnaire de Physique, Article "Alun."
HISTORY OF ALUMINIUM. 3
Returning to the time of Marggraff, we find soon after the
pubHcation of his paper indications that chemists suspected
this newly-identified earth to be a compound body, and the
search after aluminium had truly begun.
Macquer, * in 1758, wrote, "the earth of alum is white, infus-
ible, and I suspect that it has a relation more or less distant
with the metallic earths."
Baron, f a professor of chemistry in Paris, is our first re-
corded experimenter on the isolation of aluminium. In 1760
he communicated a memoir to the Academy in which he said :
" Marggrafif of Berlin has shown us what the earth of alum is
not, without showing very definitely what it is. I believe the
base of alum to be of a metallic nature, for the following
reasons: i. It has almost no properties in common with the
known earths. 2. It has analogies with the metallic earths, e. g.,
its astringent salts." Baron then proceeds to say that he had
tried all known methods of reducing this base, but without re-
sult, and concludes by saying, " If I had been fortunate enough
to reduce the base of alum to a metal, no other argument would
be needed, and that which to-day I conjecture would be a de-
monstrated fact. I am far from regarding the problem as an
impossibility. I think it not too venturesome to predict that
a day will come when the metallic nature of the base of alum
will be incontestably proven."
Baron does not record the manner in which he tried to re-
duce alumina, but it is probable that he mixed it with carbon
or some organic substance, with salt or soda for flux, and
heated as highly as possible in a charcoal fire. We neverthe-
less have his word that he tried all the methods of reduction
then known.
Lavoisier % regarded it as highly probable that alumina was
the oxide of a metal, the aflSnity of the metal for oxygen being
* Memoires de Paris, 1758.
t Memoires de 1' Acad. Royale, April l6, 1760, p. 274.
t Journal de Physique, May, 1782.
4 ALUMINIUM.
SO strong that neither carbon nor any of the reducing agents
then known was able to overcome it.
Ruprecht and Tondi,* two Austrian chemists, repeated
Baron's experiments in 1790. They thought that hitherto the
reducing agent had not been intimately enough mixed with the
alumina, and that the temperature used had not been sufficiently
high, so they mixed alumina very intimately with charcoal dust,
made it into a paste with oil, and spread it on the inner walls
of a Hessian crucible, which was finally filled up with powdered
charcoal and a layer of bone ash placed on top. Putting the
crucible in a forge, a strong fire was kept up for three hours.
As a result, small metallic particles were found on the inner
sides of the crucible. These they supposed to be the metallic
base of alumina.
Sav4resi,f in Italy, and Klaproth and Karsten, in Germany,
duplicated this experiment with similar results, and then
analyzed the globules of metal obtained. They found them to
be phosphide of iron, the iron coming from the charcoal used
and the phosphorus from the bone ash. Professor Klaproth
referred to this incident as " the pretended metallization of the
earths," and said further, " if there exists an earth which has
been put in conditions where its metallic nature should be dis-
closed, if it had such, an earth exposed to experiments suitable
for reducing it, tested in the hottest fires by all sorts of
methods, on a large as well as on a small scale, that earth is
certainly alumina, yet no one has yet perceived its metalli-
zation."
Lavoisier succeeded in melting alumina in a charcoal fire fed
by pure oxygen. Dr. Hare, in 1802, melted it with the oxy-
hydrogen blow- pipe to a white enamel, but noticed no signs of
reduction to metal.
In 1807 Sir Humphry Davy attacked the alkaline earths
with his great battery which had isolated potassium and so-
* Allgemeiner Zeitung, Nov., 1 790.
t Annales de Chimie, 1791, »., 254.
HISTORY OF ALUMINIUM. 5
dium. His first experiment, mixing alumina with red oxide of
mercury, and passing the electric current through this in con-
tact with metallic mercury, gave no result. He then melted
alumina with potash, and passed the current from 500 plates
through it. The receiving blade received a metallic coating,
and on dipping it into water the latter was decomposed, and
afterwards the solution was proved to contain alumina. An
experiment with soda gave a similar result. Davy had in fact
electrolyzed the aluminates of potassium and sodium, and ob-
tained metallic alkali and aluminium, but he was unable to
isolate the latter by any means he could devise.
Davy next tried to reduce alumina by heating it with metal-
lic potassium. Some potassium oxide was formed, showing
some reduction had taken place, but he could find no metal.
In 1809 Davy had a new battery of 1000 plates, and with it
fused iron to whiteness in the arc in contact with alumina.
The iron became somewhat whiter, and when dissolved in acids
showed that it contained aluminium. The fact was thus estab-
lished that alumina can be decomposed while fiuid in the electric
arc, and its metal alloyed with iron.
Davy next mixed alumina with potassium and iron filings,
hoping that the iron would collect any metal reduced from the
alumina. On melting this mixture a button resulted which
was white and harder than iron, and was undoubtedly an alloy
of iron and aluminium, but Davy could not separate the two
metals. In concluding the recital of his experiments he said,
" Had I been fortunate enough to isolate the metal after which
I sought, I would have given it the name alumium.
In making this suggestion it is perfectly plain that Davy in-
tended this word to represent the metal from alum, simply
starting with alum, and adding ium as the proper termination.
Objections were very soon thereafter made to this proposed
name, not to the termination ium, which was considered abso-
lutely proper, but to the root or stem of the word. It was
maintained by French, German and Swedish writers that the
name of the new metal should be derived from its oxide, and
6 ALUMINIUM.
that the stem of the word should therefore be alumin, and
thence the name aluminium. Davy was influenced by these
criticisms to the extent of changing in 1812 to alumin-um, but
no writers, except a very few English and, in recent years, some
Americans, have used this spelling.
Prof. Benj. Silliman* was in 1813 repeating Hare's experi-
ment of fusing alumina with the oxy-hydrogen blowpipe. The
alumina was supported on charcoal, and he noticed small me-
tallic globules rolling and darting out from under the fused
mass and burning with a bright light. These globules could
have been nothing else than aluminium reduced from fluid
alumitia by charcoal. The metal burnt, however, almost in-
stantly, and no globules could be obtained.
The Swedish chemist Oersted believed, in 1824, that he had
isolated aluminium. He used anhydrous aluminium chloride
as a starting point, and heated it with potassium amalgam,
thinking that the potassium would reduce the chloride and
leave an amalgam of aluminium and mercury, from which the
latter could be distilled away. Potassium, however, when
amalgamated with mercury is not powerful enough to reduce
aluminium chloride, although it can reduce it if used alone, and
so Oersted missed, by a very little, the honor of first isolating
aluminium.
Berzelius was also a worker on the aluminium problem. He
wrote to Sir Humphry Davy, in 1809, that he had reduced
alumina by heating it with carbon in the presence of iron, but
it is probable that he found himself mistaken, as he does not
refer to this matter in any of his later writings ; once, however,
he came within a very little of succeeding. He had studied
the composition and formula of the mineral cryolite, had made
it artificially, and also the corresponding potassium salt. It
then occurred to him that this latter salt might be reduced by
metaUic potassium. He made the experiment in a crucible,
carefully washed the fusion with water, but found no metal. It
* Memoirs Connecticut Acad, of Arts and Science. Vol. I, 1813.
HISTORY OF ALUMINIUM. 7
is quite evident that his sole mistake was in using an excess of
potassium, which, after the reduction, gave on sokition in water
a caustic alkah sokition, which immediately dissolved all the
reduced aluminium. Had he used an excess of the fluoride
salt, the story would almost certainly have read difTerently, be-
cause this reduction has since then been repeatedly performed.
The date of this experiment was 1825.
In 1827, Frederick Wohler, Professor of Chemistry at the
University of Gottingen, after repeating Oersted's experiment
with unsatisfactory results, modified the experiment by using
FREDERICK WOHLER.
pure potassium as the reducing agent, instead of its amalgam.
He obtained a grey, metallic powder, which was finely-divided
aluminium. He was unable to melt this powder into a button,
so as to determine its properties en masse, but he described many
of its chemical properties, and produced from it some alumin-
ium compounds which had not been before made, such as the
sulphide and arsenide. This powder was not absolutely pure
aluminium, as it contained a little platinum from the crucible
in which the reduction was performed, and some potassium,
which lessened its resistance to chemical agents. At that time
8 ALUMINIUM.
no further use was made of these facts. Later, in 1845, on
making vapor of aluminium chloride pass over potassium
placed in platinum boats, Wohler obtained the metal in small
malleable globules of metallic appearance, from which he was
able to determine the principal properties of aluminium. But
the metal thus obtained was scarcely as fusible as cast iron,
without doubt because of the platinum with which it had
alloyed during its preparation. In addition to this, it decom-
posed water at io6°C, from which we suppose that it was still
impregnated with potassium or aluminium chloride. It is to
H. ST. CLAIRE DKVIIXE.
H. St. Claire Deville that the honor belongs of having, in 1854,
isolated aluminium in a state of almost perfect purity, deter-
mining its true properties.
Thus, while aluminium had been isolated in 1827, for
eighteen years its properties en masse were unknown, and it
was only at the end of twenty-seven years after its discovery
that the true properties of the pure metal were established by
Deville. The second birth of aluminium, the time at which it
stepped from the rank of a curiosity into the number of the
useful metals, dates from the labors of Deville in 1854. If
HISTORY OF ALUMINIUM. 9
Wohler was the discoverer of aluminium, Deville was the
founder of the aluminium industry.
In commencing researches on aluminium, Deville, while he
applied the method of Wohler, was ignorant of the latter's results
of 1845. Besides, he was not seeking to produce aluminium
that he might turn its valuable properties to practical account,
but that it might serve for the production of aluminium prot-
oxide (AlO), which he believed could exist as well as ferrous
oxide (FeO). The aluminium he wished to prepare would, he
thought, by its further reaction on aluminium chloride, form
aluminium proto-chloride (AlCP), from which he might derive
the protoxide and other proto-salts. But on passing vapor of
aluminium chloride over the metallic powder formed by reduc-
tion by potassium, this proto-chloride was not thus produced;
he obtained, inclosed in a mass of aluminium-potassium chlo-
ride (AICI3.KCI), fine globules of a brilliant substance, ductile,
malleable, and very light, capable of being melted in a mufifle
without oxidizing, attacked by nitric acid with diflSculty, but
dissolved easily by hydrochloric acid or caustic potash with
evolution of hydrogen.
Deville troubled himself no more about the proto-salts of
aluminium, but, recognizing the importance of his discovery,
turned his attention to preparing the metal. He was at this
time Professor of Chemistry in the Ec^le Normale, Paris ; his
salary was but 3000 francs, his estate was small, and he was
practically without the means of doing anything further.
On Monday, February 6, 1854, Deville read at the .seance of
the Academy a short paper entitled "Aluminium and its Chemi-
cal Combinations," in which he explained the results of this
experiment as showing the true properties of aluminium,
and also furnishing a method of purifying it, and declared his
intention of commencing immediate search for a process which
could be economically applied on a commercial scale. M.
Thenard, at the close of the communication, remarked that such
experiments ought to be actively pursued, and that, since they
were costly, he believed the Academy would hasten the accom-
lO ALUMINIUM.
plishment of the work by placing at Deville's disposal the neces-
sary funds. As the outcome of this, the Academy appointed
Deville one of a committee to experiment on producing alumin-
ium, and 2000 francs were placed at his disposal for the work.
It was on the occasion of the reading of this paper that M.
Chenot addressed a note to the Academy on the preparation
of aluminium and other earthy and alkaline metals, in which he
claimed, in some regards, priority for his inventions. (See
further under "Reduction by Carbon.") This note was re-
served to be examined by a commission appointed to take
notice of all communications relative to the production of
aluminium.
With the funds thus placed at Deville's disposal, he experi-
mented at the Ecole Normale for several months. As potas-
sium is very dangerous to handle, cost then 900 francs a kilo,
and gives comparatively but a small return of aluminium, De-
ville, in view of the successful work of Bunsen on the electric
decomposition of magnesium chloride, tried first the reduction
of aluminium chloride by the battery. On March 20, 1854,
Deville announced to the Academy in a letter to Dumas that
he had produced aluminium without alkaline help, and sent a
leaf of the metal thus obtained. At that time Thenard, Boussin-
gault, Pelouze, Peligot, and later, de-la-Rive, Regnault, and
other well-known scientists, shared the honor of assisting in the
laboratory experiments. Deville sent, in the following May, a
mass of five or six grammes weight to Liebig, making no secret
of the fact that it was reduced by the battery ; while Balard at
the Sorbonne, and Fremy at the Ecole Polytechnique, publicly
repeated his experiments and explained them in all their de-
tails. Although these experiments succeeded quite well, yet
because of the large consumption of zinc in the battery used
the process could evidently not be applied industrially, and
Deville felt obliged to return to the use of the alkaline metals.
Towards the middle of 1854 Deville turned to sodium, with-
out a knowledge of those properties which render it so prefer-
able to potassium, but solely because of its smaller equivalent
HISTORY OF ALUMINIUM. I I
(23 to that of potassium 39) and the greater cheapness of soda
salts. He studied the manufacture of sodium, with the aid of
M. Debray, in his laboratory at the Ecole Normale, and their
experiments were repeated at Rousseau Bros.' chemical works
at Glaciere, when they were so successful that Rousseau Bros,
very soon put metallic sodium on the market at a much reduced
price. It is said that while metallic sodium was a chemical
curiosity in 1855, costing something like 2000 francs a kilo, its
cost in 1859 is put down at 10 francs. Deville carried this pro-
cess to such perfection that for twenty-five years it remained
almost precisely at the status in which he left it in 1859. In
order to still further cheapen aluminium, Deville busied himself
with the economic production of alumina, which gave later a
lively impulse to the cryolite and bauxite industries.
On August 14, 1854, Deville read a paper before the Acad-
emy describing his electrolytic methods at length (see under
"Reduction by Electricity"), showing several small bars of the
metal, and also stating some of the results already achieved by
the use of sodium, but not going into details, since he believed
that numerous analyses were necessary to confirm these results
— which he was unable to have made with the funds at his dis-
posal. He also stated that the desire to show, in connection
with his assertions, interesting masses of the metal, alone pre-
vented the earlier publication of the methods used. Several
days before this, Bunsen published in Poggendorif's Annalen
a process for obtaining aluminium by the battery, which re-
sembled Deville's method, but of which the latter was ignorant
when he read his paper. Thus it is evident that the isolation
of aluminium by electrolysis was the simultaneous invention of
Deville and Bunsen.
After reading this paper, Deville caused a medal of alumin-
ium to be struck, which he presented to the Emperor Na-
poleon III. The latter, looking forward to applying such a
light metal to the armor and hemlets of the French Cuirassiers,
immediately authorized experiments to be continued at his own
expense on a large scale. This anticipation ultimately proved
12 ALUMINIUM.
impracticable, but the ambition in which it was bred was caused
for once to minister to the lasting benefit of mankind. Deville,
however, about this time accepted, in addition to his duties as
professor at the Ecole Normale, a lectureship at the Sorbonne
(where he afterwards obtained a full professorship), and it was
not until March of the next year that the experiments at the
cost of the Emperor were begun.
It was about August, 1854, that two young chemists, Chas.
and Alex. Tissier, at the suggestion of Deville, persuaded M.
de Sussex, director of a chemical works at Javel, to let them
experiment in his laboratory (of which they had charge) on
the production of sodium.
Towards the commencement of 1855, Deville took up the in-
dustrial question, the Emperor putting at his disposition all the
funds necessary for the enterprise, and in March the investigator
went to work and installed himself at the chemical works at
Javel in a large shed which the director, M. de Sussex, kindly
put at his service.
The investigations were carried on here for nearly four
months, ending June 29th, and the process elaborated was an
application on a large scale of the experiments he had made at
the expense of the Academy, which he described in his paper
of August 14, 1854, and by which he had been able to obtain
a few pencils of metal. In this work such success attended his
efforts that on June 18 Deville presented to the Academy
through M. Dumas large bars of pure aluminium, sodium, and
masses of aluminium chloride. The members and large audi-
ence were loud in their admiration and surprise at the beauty
of the metal. Dumas stated that the experiments at Javel had
put beyond a doubt the possibility of extracting aluminium on
a large scale by practical processes. Deville's paper was then
read, describing all his processes in detail, and concluding with
the following words : " After four months of work on a large
scale, undertaken without responsibility on my part, and, in
consequence with the tranquility and repose of mind which are
so often wanting to the investigator, without the preoccupation
HISTORY OF ALUMINIUM. 1 3
of expense, borne by His Majesty the Emperor, whose gen-
erosity had left me entire liberty of action, encouraged each
day by distinguished men of science, I hope to have placed the
aluminium industry on a firm basis."
It was the metal made at this time at Javel which was ex-
hibited at the Paris Exposition in 1855. In the Palais de I'ln-
dustrie, among the display from the porcelain works at Sevres,
were ingots and some manufactured objects. The first article
made of aluminium was, in compliment to the Emperor, a baby-
rattle for the infant Prince Imperial, for which purpose it must
have served well, because of the sonorousness of the metal.
After terminating these experiments Deville continued work-
ing at the Ec61e Normale, the Emperor defraying his expenses,
until April, 1856. The memoir published in the Ann. de Chim.
et de Phys., April, 1856, contains, besides the results obtained
at Javel, the improvements devised in the meantime.
It appears that when Deville first went to Javel, he had for
assistants the Tissier Brothers, who were charged by M. de
Sussex to give him all the aid they could. Since the previous
autumn the Tissiers had been experimenting on sodium fur-
naces, and now, in concert with Deville, they drew up plans for
furnaces, and aided in devising other apparatus. Under these
circumstances the furnace for the continuous manufacture of
sodium in cylinders was devised, which the Tissiers claim De-
ville strongly advised them to make their property by patenting,
asking only from them the use of it for his experiments. So,
immediately after the experiments were ended, in July, the
Tissiers patented the furnace in question, and, leaving Paris,
took charge of M. Chanu's works at Rouen. On the other
hand, Deville always reproached them for acting in bad faith.
He says that after having assisted for about two months in set-
ting up his apparatus, being forced to leave the works because
of misunderstandings between them and M. de Sussex, they
were admitted to his laboratory at the Ecole Normale, and
initiated by him into the knowledge of all those processes
which they made use of afterwards, then suddenly left, taking
14 ALUMINIUM.
drawings of furnaces, details of processes, etc., which they not
only made free use of, but even patented. However, whichever
party was in the right (and those who comprehend the char-
acter of Deville can hardly doubt which was), the fact stands
that in July, 1855, M. Chanu, an honorable manufacturer of
Rouen, founded a works in which Deville's processes were to
be applied, and intrusted the direction of it to the Tissier
Brothers.
The history of the works at Rouen is thus described by the
Tissiers in their book on aluminium, of which we shall speak a
little further on :
"la July, 185s, Messrs. Maletra, Chanu, and Davey, of
Rouen, formed a company to produce aluminium, and we were
intrusted with the organization and special charge of the in-
dustry. The commencement was beset with difficulties, not
only in producing, but in using the metal. It then sold at $200
per kilo, the price being an insurmountable obstacle to its em-
ployment in the arts. The small capital at our disposal was
not enough to start the industry, to pay general expenses, and
the losses occasioned by the many experiments necessary. On
February 28, 1856, the society was dissolved. In April of the
same year, M. William Martin, struck by the results already
obtained and sanguine of greater success, united with us. From
that time daily improvements confirmed M. Martin's hopes,
and in 1857 the works at Amfreville-la-mi-Voie, near Rouen,
sold the metal at $60 per kilo ($2 per oz.). The laboratory
of this works was devoted to researches on everything concern-
ing the production and application of aluminium. M. Martin
has our sincere gratitude for the kindness with which he so
willingly encouraged and contributed to the progress of the
manufacture of this wonderful metal."
The process ultimately used at Amfreville was the reduction
of cryolite by sodium, but the enterprise was not a permanent
success, and after running for a few years it was abandoned and
the works closed.
Returning to Deville, we find that after leaving Javel one of
HISTORY OF ALUMINIUM. I 5
the first subjects he investigated was the use of cryolite for
producing aluminium. The researches made with the aid of
MM. Morin and Debray were published in the memoir of April,
1856, and became the basis of the process carried out by the
Tissiers at Rouen. Besides this, Deville perfected many of the
details of a practical aluminium plant, with the result that in
the spring of 1856 he united with Messrs. Debray, Morin, and
Rousseau Bros, (the latter manufacturers of chemicals at Gla-
ciere, in whose works aluminium had been made since the
middle of 1855) and put up new apparatus in the works at
Glaciere, the company furthering the work entirely at their own
cost. This enterprise lasted for more than a year, during which
a number of processes were tried and continued improvements
made, so that towards August of the same year aluminium
was put on the market in Paris at 300 francs a kilo, being one-
third what it cost a year previous.
Finally, in April, 1857, the little works at Glaciere, a suburb
of Paris, in the midst of gardens and houses, and turning into
the air fumes charged with chlorine and salts, was obliged by
reason of general complaints to stop making aluminium. The
plant was moved to Nanterre, where it remained for some years,
under the direction of M. Paul Morin, being on a scale four
times as large as the actual demand. Afterwards part of the
plant was moved to the works of H. Merle & Co., at Salindres,
and later on the whole plant, where the manufacture was until
recently carried on by Pechiney & Co. The works at Nan-
terre were really the only "aluminium works" built by Deville,
the others were plants installed at general chemical works ; but
these at Nanterre were built by the united efforts of Deville,
his brothers and parents, and a few personal friends. Among
those who aided Deville, especially in the problems which the
new industry presented, he speaks warmly of Messrs. d'Eichtal,
Lechatelier, and Jacquemont.
In 1858 the Tissiers wrote and published- a small work
entitled " Recherches sur 1' Aluminium." which, in view of what
Deville could have written about the subject, was a decided
l6 ALUMINIUM.
misrepresentation of the results which had been thus far accom-
plished. Deville thought that the industry was yet too young
to merit any sort of publication, yet he naively writes in his
work "De 1' Aluminium," in 1859, "I will sincerely acknowl-
edge that my writing is a little due to my pride, for I decided
to take the pen to speak of my work, only to avoid seeing it
belittled and disfigured as it has been lately in the book written
by MM. Tissier."
Deville published his book in September, 1859, and he con-
cludes it with these words : " I have tried to show that alumin-
ium may become a useful metal by studying with care its
physical and chemical properties, and showing the actual state
of its manufacture. As to the place which it may occupy in
our daily life, that will depend on the public's estimation of it
and its commercial price. The introduction of a new metal
into the usages of man's life is an operation of extreme diffi-
culty. At first aluminium was spoken of too highly in some
publications, which made it out to be a precious metal, but
later these estimates have depreciated even to the point of con-
sidering it attackable by pure water. The cause of this is the
desire which many have to see taken out of common field-mud
a metal superior to silver itself ; the opposite opinion established
itself because of very impure specimens of the metal which were
put in circulation. It seems now that the intermediate opinion,
that which I have always held and which I express in the first
lines of my book, is becoming more public, and will stop the
illusions and exaggerated beliefs which can only be prejudicial
to the adoption of aluminium as a useful metal. Moreover,
the industry, established as it now is, can be the cause of loss
to no one ; as for myself, I take no account of the large part of
my estate which I have devoted, but am only too happy if my
efforts are crowned with definite success, in having made fruit-
ful the works of a man whom I am pleased to call my friend,
the illustrious Wohler."
Contemporary with the early labors of Deville, among the
numerous chemists and metallurgists investigating this attract-
HISTORY OF ALUMINIUM. 1 7
ive field, we find Dr. Percy in England and H. Rose in Ger-
many, whose experiments on the reduction of cryolite by
sodium were quite successful, and are herein described later on.
As early as 1856 we find an article in an American magazine *
showing that there were already chemists in the United States
spending time and money on this subject. The following is the
substance of the article alluded to: "Within the last two years
Deville has extracted 50 to 60 lbs. of aluminium. At the pres-
ent time, M. Rousseau, the successor of Deville in this manu-
facture, produces aluminium which he sells at $100 per pound.
No one in the United States has undertaken to make the metal
until recently Mons. Alfred Monnier, of Camden, N. J., has,
according to the statement of Prof. James C. Booth in the
" Penn. Inquirer," been suceessful in making sodium by a con-
tinuous process, so as to procure it in large bars, and has made
aluminium in considerable quantity, specimens of which he has
exhibited to the Franklin Institute. Mons. Monnier is desirous
of forming a company for the manufacture of aluminium, and is
confident that by operating in a large way he can produce it at
a much less cost than has heretofore been realized. We would
suggest the propriety of giving aid to this manufacture at the
expense of the government, for the introduction of a new metal
into the arts is a matter of national importance, and no one can
yet realize the various and innumerable uses to which this new
metal may be applied. It would be quite proper and constitu-
tional for Congress to appropriate a sum of money, to be ex-
pended under the direction of the Secretary of the Treasury in
the improvement of this branch of metallurgy, and in testing
the value of the metal for coinage and other public use."
In the next volume of the "Mining Magazine"! there is a
long article by Mr. W. J. Taylor, containing nothing new in
regard to the metallurgy of aluminium, but chiefly concerned
in calculating theoretically the cost of the metal from the raw
* Mining Magazine,. 1856, vii., 317.
t Mining Magazine, viii., 167 and 228. Proc. Ac. Nat. Sci., Jan., 1857.
2
1 8 ALUMINIUM.
materials and labor required by Deville's processes, and con-
cluding that it was quite possible to make it for $ i .00 per pound.
In 1859 the first aluminium works in England were started at
Battersea, near London, by C. H. Gerhart, using Deville's pro-
cess. No details are obtainable respecting the size of this
works. M. Henri Brivet informs me that they had no connec-
tion with Bell Bros.' enterprise, started the next year after, and
that they closed operations about 1865.
In i860, Bell Bros, established a plant at Washington, near
Newcastle-on-Tyne, with the immediate co-operation of Deville.'
In 1862 this company was selling aluminium at 40 shiUings per
troy pound, and they continued operations until 1874, when
they closed because the business was no longer profitable.*
It was probably shortly after 1 874 that the large firm of J. F.
Wirtz & Co., Berlin, made an attempt to start an aluminium
works. The project drooped before it was well started ; and it
is only within the last few years that Germany has possessed a
flourishing aluminium industry.
The further we get away from an age the better able are we
to write the true history of that age. And so as years pass
since the labors of Wohler, Deville, and Tissier, we are now
able to see better the whole connected history of the develop-
ment of this art. Dr. Clemens Winckler gives us a compre-
hensive retrospect of the field seen from the standpoint of 1879,
from which we condense the following : -j- " The history of the
art of working in aluminium is a very short one, so short that
the present generation with which it is contemporary is in dan-
ger of overlooking it altogether. The three international exhi-
bitions which have been held in Paris since aluminium first
began to be made on a commercial scale form so many memo-
rials of its career, giving as they did at almost equal intervals
evidence of the progress made in its application. In 1855 we
meet for the first time in the Palais de 1' Industrie with a large
* Personal communication to the writer from Sir Lowthian Bell,
t Industrie Blatter, 1879; Sci. Am. Suppl., Sept. 6, 1879.
HISTORY OF ALUMINIUM. 1 9
bar of the wonderful metal, docketed with the extravagant
name of the ' silver from clay.' In 1 867 we meet with it again
worked up in various forms, and get a view of the many diffi-
culties which had to be overcome in producing it on a large
scale, purifying and moulding it. We find it present as sheets,
wire, foil, or worked-up goods, polished, engraved, and soldered,
and see for the first time its most important alloy, aluminium
bronze. After a lapse of almost another dozen years we see at
the Paris Exhibition of 1878 the maturity of the industry. We
have passed out of the epoch in which the metal was worked
up in single specimens, showing only the future capabilities of
the metal, and we see it accepted as a current manufacture
having a regular supply and demand, and being in some re-
gards commercially complete. The despair which has been
indulged in as to the future of the metal is thus seen to have
been premature. The manufacture of aluminium and goods
made of it has certainly not taken the extension at first hoped
for in its behalf ; the lowest limit of the cost of manufacture was
soon reached, and aluminium remains as a metal won by ex-
pensive operations from the cheapest of raw materials.
" There are several reasons why the metal is shown so little
favor by mathematical instrument makers and others. First of
all, there is the price ; then the methods of working it are not
everywhere known ; and further, no one knows how to cast it.
Molten aluminium attacks the common earthen crucible, re-
duces silicon from it, and becomes gray and brittle. This
inconvenience is overcome by using lime crucibles, or by lining
an earthen crucible with carbon or strongly burnt cryoHte clay.
If any one would take up the casting of aluminium and bring it
into vogue as a current industrial operation, there is no doubt
that the metal would be more freely used in the finer branches
of practical mechanics."
At the time of Dr. Winckler's writing, the extraction of
aluminium in France was carried on by Merle & Co., at Salin-
dres, while the Societe Anonyme de 1' Aluminium, at Nanterre,
worked up the metal. Both firms were represented at the Ex-
20 ALUMINIUM.
position of 1878. The prices quoted then were 130 francs a
kilo for aluminium, and 18 francs for 10 per cent, aluminium
bronze. From 1874, when Bell Bros.' works at Newcastle-on-
Tyne stopped operations, until 1882, when a new enterprise
was started in England by Mr. Webster, the French company
were the only producers of aluminium.
Regarding the prospects of the aluminium industry at this
period, we can very appropriately quote some remarks of the
late Mr. Walter Weldon, F. R. S., who was a personal friend of
M. Pechiney (director of the works at Salindres), had given
great attention to aluminium, and was considered as a first
authority on the subject. Speaking in March, 1883, before the
London Section of the Society of Chemical Industry, he stated
that the only method then practiced for the manufacture of
aluminium was DeviUe's classical one; that at Salindres, M.
Pechiney had improved and cheapened it, but that was all the
progress made in the industry in twenty-five years. Continu-
ing, Mr. Weldon outlined the possible lines on which improve-
ments might be made, as :
1st. Cheapening the production of aluminium chloride, or of
aluminium-sodium chloride.
2d. Substituting for these chlorides some other cheaper
anhydrous compounds of aluminium not containing
oxygen.
3d. Cheapening sodium.
4th. Replacing sodium by a cheaper reducing agent.
Mr. Weldon exhibited the relative cost of the materials used
in making aluminium, as then carried on by M. Pechiney, as :
Producing the alumina 10 per cent.
" " double chloride 33 "
" " sodium and reducing therewith 57 "
"Discussing these figures, it is seen that the cost of the alu-
mina forms but a small item in the cost of the metal, since a
saving of 50 per cent, in its cost would only cheapen the metal
5 per cent. A large margin is, however, left in the conversion
HISTORY OF ALUMINIUM. 2 1
of the alumina into the chloride, and it is here that a large sav-
ing may be expected, either in cheaper methods of producing
the chloride or by the substitution of some other cheaper salt
for the chloride. The only other suitable compounds which
might replace the latter are the fluoride, iodide, bromide, sul-
phide, phosphide, or cyanide. The fluoride has been used to
some extent in the form of cryolite, but, from the impurities in
the mineral and its corrosive action on the apparatus used for
reduction, the metal produced is very much contaminated with
iron and silicon. The bromide and iodide, no matter how pro-
duced, would always be too costly to replace the chloride. The
production of the sulphide in a suitable form from which the
metal can be extracted has thus far not proved a success, and
even if ever it be thus produced in a suitable condition, it is not
at all likely to be as cheap a material to use as the chloride.
The phosphide and cyanide can thus far only be produced from
the metal itself, and are, therefore, totally out of the question.
To find a substitute for sodium as a reducing agent has been a
favorite object of research among chemists for the past thirty
years, and although every element occurring in any abundance,
or obtainable at a cheaper rate than sodium, has been tried
under almost all conditions, yet absolutely nothing has been
accomplished in this direction that would entitle any one to the
belief that aluminium can ever be produced chemically without
the use of sodium. So absorbing to those interested in the
search for a substitute for sodium has the occupation proved,
that the effort to cheapen sodium did not receive anything like
its fair share of attention. Since of the 57 per cent, ascribed
to the cost of sodium and reduction, 50 per cent, represents the
sodium, which thus costs about six shillings a pound, there is
seen to be a very large margin for improvements, since the raw
materials for a pound of sodium do not cost over i or at most
2 shillings."
In 1882 the cost of aluminium was materially cheapened by
the applications of the inventions of Mr. Webster, which, in ac-
cordance with the analysis of the problem made by Mr. Weldon,
2 2 ALUMINIUM.
consisted principally in the cheap production of alumina and its
conversion into chloride. Mr. Webster had experimented on
this subject many years, and in 1881 and 1882 took out patents
for his processes, and organized the "Aluminium Crown Metal
Company," located at Hollywood, near Birmingham, where
several thousand pounds were expended in plant. Business
was soon commenced on a large scale, the company produc-
ing, however, many other alloys besides those of aluminium.
The business grew until it soon became the serious competitor
of the French company, and practically controlled the English
market. However, a radical change of still greater importance
in the sodium process was made in 1886 by an invention of
Mr. H. Y. Castner, of New York City. This gentleman con-
ceived the plan of reducing sodium compounds in cast-iron
pots, from a fused bath of caustic soda, by which the reduction
is performed at a much lower temperature, and the yield of
sodium is very much more than by the Deville method. The
application of this process on a large scale, with the use of gas
furnaces and other modern improvements, has lowered the cost
of sodium from $1 per pound to about 20 or 25 cents. It is
but just to say that Mr. Castner's invention was by no means a
chance discovery. For four years he worked in a large labor-
atory fitted up for this special purpose, and after many dis-
couragements in trying to produce aluminium by means other
than that of sodium, was led finally to consider that the cheap-
ening of this metal was the most promising method for cheap-
ening aluminium, and after much patient, hard work, success
was at last reached.
Mr. Castner's patent was taken out in the United States in
June, 1 886, and, while being the first one granted on that sub-
ject in this country, is said also to be the only one taken out in
the world since 1808. With the assistance of Messrs. J. H. and
Henry Booth, of New York City, Mr. Castner demonstrated the
process by building and operating a furnace on a somewhat
large scale. This being accomplished, Mr. Castner crossed to
England and met the representatives of the Webster process.
HISTORY OF ALUMINIUM. 23
with whom it was evident a combination would be especially
advantageous to both parties ; for, with cheap aluminium chlor-
ide and cheap sodium, it was clear that a strong process could
be built up. Mr. Castner then demonstrated plainly, by erect-
ing a furnace and operating it for several weeks, that his pro-
cess was all that he claimed for it. As a result of this success,
the "Aluminium Company, Limited," was incorporated in June,
1887, with a share capital of .£'400,000, " to acquire the patents
and work and develop the inventions of James Webster for the
manufacture of pure alumina and certain metallic alloys and
compounds, together with the business at present carried on by
the Webster Patent Aluminium Crown Metal Company, Lim-
ited, in Birminghami, Sheffield, and London, England, and also
to acquire the patents and work and develop the invention of
H. Y. Castner for the manufacture of sodium and potassium."
Mr. Webster was paid ;£'2 30,000 for the business, properties,
stock, etc., of the Crown Metal Company, while ;£'i40,ooo was
allowed for the sodium patents. The new company appointed
Mr. Castner managing director, and the erection of large works
was immediately begun at Oldbury, near Birmingham. These
works were started in operation at the end of July, 1888. They
covered five acres of ground, and their daily production for
some time was about 250 pounds, which was sold at 20 s. per
pound. This was increased during 1889 to nearly 500 pounds
a day, and the selling price of the aluminium decreased to 16
shillings. Early in 1891, however, this company was forced to
stop the manufacture of aluminium, as its selling price was re-
duced by the owners of the electrolytic processes below 4 shil-
lings per pound, at which price the sodium processes could no
longer compete. The company continued in the sodium busi-
ness, and in 1893, with their original capital of .£400,000 writ-
ten down to ;£^8o,ooo, we hear that they are doing a prosperous
business under Mr. Castner's direction, producing sodium and
sodium peroxide, and making caustic soda and bleaching
powder by electrolysis of common salt. In view of the promi-
nent part which this works took in the aluminium industry from
24 ALUMINIUM.
1888 to 1 89 1, and as an acknowledgment to Mr. Castner's able
direction, the methods there used have been rightly designated
as " The Deville-Castner Process."
We have followed the progress of the Webster and Castner
processes up to the date of starting the works at Oldbury, be-
cause the continuity of the advances made in the old Deville
process would hardly allow of a break in order to mention
other processes arising meanwhile. However, the years since
1884 have witnessed not one but several revolutions in the alu-
minium industry. The great advances made in dynamo-electric
machinery in the last decade have led to the revival of the old
methods of electrolysis descovered by Deville and Bunsen, and
to the invention of new methods of decomposing aluminium
compounds electrolytically. It will be recalled that the first
small pencils of aluminium made by Deville were obtained by
electrolysis, and that he turned back to the use of the alkaline
metals solely because the use of the battery to effect the de-
composition was far too costly to be followed industrially.
This fact still holds true, and we cannot help supposing that if
Deville had had dynamos at his command such as we have at
present, the time of his death might have seen the aluminium
industry far ahead of where it now is.
First in point of time we notice Gratzel's process, patented in
Germany in 1883 and used industrially by the "Aluminium and
Magnesium Fabrik, Patent Gratzel," at Hemelingen, near Bre-
men. The process was essentially the electrolysis of a bath of a
fused aluminium salt, such as chloride or fluoride, the improve-
ments on the older experiments being in details of apparatus
used, the use especially of anodes of mixed carbon and alu-
mina, and the use of dynamic electricity. Several metallurgists
maintained the uselessness of the Gratzel processes, and their
position was proved to be not far from the truth, for in October,
1887, the company announced that the addition " Pt. Gratzel"
would be dropped from the firm name, since they had aban-
doned Gratzel's processes and were making aluminium by
methods devised by Herr Saarburger, director of their works.
HISTORY OF ALUMINIUM. 25
The processes of this latter gentleman not being published, we
are unable to state their nature, but they were very probably
electrolytic. In October, 1888, Mr. Saarburger reported that
their works were producing at the rate of 12,000 kilos of alu-
minium yearly, besides a large quantity of aluminium bronze
and ferro-aluminium. The firm also worked up the aluminium
and its alloys into sheet, wire, tube, etc.
Since 1890, however, this company has retired from the alu-
minium business, their works being now used only for the pro-
duction of magnesium.
A somewhat similar electrolytic process was patented by Dr.
Ed. Kleiner, of Zurich, in 1886. Molten cryolite was decom-
posed by two carbon poles, the heat generated by the current
first melting the cryolite and then electrolyzing it. Since the
motive power in this, as in all electric processes, composes one
of the chief elements for carrying on the reduction, the Kleiner
Gesellschaft, formed to work this method, made an attempt to
obtain water rights at the falls of the Rhine, at Schaffhauseni
which would furnish 15,000 horse-power. This proposition
being refused by the government, an experimental plant was
started at the Hope Mills, Tyddesley, Lancashire, England.
The results were not encouraging enough to allow of commer-
cial success, and the process was abandoned.
An electrolytic method, different in principle from both the
preceding, is the invention of Mr. Chas. M. Hall, of Oberlin,
Ohio, which was patented in the United States in April, 1889,
but applied for in 1886. The principle involved is the electric
decomposition of alumina, dissolved in a fused bath of the
fluorides of aluminium and other bases, the current reducing
the dissolved alumina without affecting the solvent. This
method is essentially different from any of the previous elec-
trical processes, which contemplated and operated simply the
decomposition of a molten aluminium salt, such, for instance, as
the solvent used by Mr. Hall. The knowledge that the fused
fluorides dissolve large quantities of alumina, and that the elec-
tric current will act on this dissolved alumina without decom-
26 ALUMINIUM.
posing the solvent, was the essence of Hall's invention, and the
source of another revolution in the aluminium industry. The
process has been operated by the Pittsburgh Reduction Com-
pany, from 1889 to 1891, in Pittsburgh, Pa., since 1891 at New
Kensington, Pa., on the banks of the Allegheny river, eighteen
miles above Pittsburgh. During 1889 this company produced
about 75 pounds of aluminium a day, which they sold at $4.50
per pound ; in 1 890 their capacity was increased to 400 poun'ds
per day, and the selling price reduced to $2.00 per pound;
since 1892 the works ha,ve been again enlarged to a capacity of
nearly one ton per day, and the selling price has tended stead-
ily downwards until it is at present $0.50 per pound. During
189s this company expects to put into operation a very large
new plant at Niagara Falls, using power generated by the new
tunnel. This works will utilize up to 6,000 horse-power, and
will have a capacity when in full operation of 6,000 to 8,000
pounds per day. This improvement will place the United
States in the front as the largest aluminium-producing country
in the world.
In France, Adolphe Minet, a well-known electrician, experi-
mented during 1887 and 1888 on the electrolysis of a molten
bath containing aluminium fluoride and sodium chloride, fed
by the addition of alumina and aluminium fluoride. From
1888 to 1 89 1 this process was run on an experimental scale
at the works of Bernard Bros., at Creil, making about 35 pounds *
of aluminium per day. In 1890 a larger plant was put up, run
by water power, at Saint Michel, Savoy, having a much larger
capacity, which it is stated had been increased in 1894 to
1,000 pounds per day. In 1895, this plant has been acquired
by a French company who will operate by the Hall process.
While the electrolytic processes so far considered use a fluid
bath, and operate at moderate temperatures with a current of
moderate intensity, there have been devised two other promi-
nent processes which operate in a somewhat different manner
and attain to economical results. These primarily depend on
the enormous temperature attainable by the use of a powerful
HISTORY OF ALUMINIUM. 2/
electric arc, and secondarily on the reduction of alumina (which
at the temperature attained becomes fluid) either by the reduc-
ing action of the carbon present or by simple electric decompo-
sition. Which of these two agencies performs the reduction, in
either process, is still an unsettled question, which we will dis-
cuss later on.
Before going further with the history of these two processes,
Cowles' and Heroult's, it may not be inappropriate to take note
of a few facts antecedent to their appearance. It is well known
that Sir W. Siemens devised an electric furnace in which the
heat of the arc was utilized for melting steel. In 1882 Mr.
Ludwig Grabau, in Hanover, Germany, purchased a Siemens
furnace for the express purpose of attempting the reduction of
alumina, and after experimenting successfully for some time,
modified the apparatus so as to work it continuously, and there-
with made aluminium alloys ; but on account of the difficulties
of the process, and the impurity of the alloys produced, Mr.
Grabau gave up the experiments, having come to the conclu-
sion that aluminium alloys to be technically valuable should be
obtained in a state of almost chemical purity. In the beginning
of 1885 Dr. Mierzinski, in his book on aluminium, presented
some very striking remarks on the use of the electric furnace,
which are so much to the point that they are well worth quoting
in this connection : " The application of electricity for produc-
ing metals possesses the advantage not to be ignored that a de-
gree of heat may be attained with it such as cannot be reached
by a blowpipe or regenerative gas-furnace. The highest furnace
temperature attainable is 2500 to 2800° C., but long before this
point is reached the combustion becomes so languid that the
loss of head by radiation almost equals the production of heat
by combustion, and hinders a further elevation of temperature.
But in applying electricity the degree of heat attainable is theo-
retically unlimited. A further advantage is that the smelting
takes place in a perfectly neutral atmosphere, the whole opera-
tion going on without much preparation, and under the eyes of
the operator. Finally, in ordinary furnaces, the refractory
28 ALUMINIUM.
material of the vessel must stand a higher heat than the sub-
stance in it, whereas by smelting in an electric furnace the
material to be fused has a higher temperature than the crucible
itself. Since the attempt to produce aluminium by the direct
reduction of alumina by carbon is considered by metallurgists
as impossible, because the temperature requisite is not attain-
able, the use of the electric current for attaining this end seems
to be of so much the more importance."
The Cowles invention was patented August i8, 1885, and
was first publicly described before the American Association
for the Advancement of Science, at their Ann Arbor meeting,
August 28, 1885. The process is due to two Cleveland gen-
tlemen, E. H. and A. H. Cowles, who in the development of
their process associated with them Prof. Charles F. Mabery, of
the Case School of Applied Science, Cleveland, as consulting
chemist. The Cowles Electric Smelting and Aluminium Com-
pany, formed to work the process, erected a plant at Lockport,
N. Y., where a water power of 1200 horse-power was secured,
and where, among other novel apparatus, the largest dynamo
in the world, made especially for this purpose by the Brush
Electric Company, was in operation. Following the success of
this plant in America, the Cowles Syndicate Company, organ-
ized to work the patents in England, put in operation works at
Stoke-on-Trent which had a capacity of something like 300
lbs. of alloyed aluminium daily. Springing also from the
Cowles process is the "Aluminium Brass and Bronze Com-
pany," of Bridgeport, Conn., which was organized in July,
1887, and controls the exclusive rights under the Cowles
American patents of manufacturing the alloys of aluminium
into sheet, rods, and wire. The extensive plant of this com-
pany employs 300 men, and has been erected at a cost of nearly
$300,000.
The principle made use of in the Cowles process is, briefly,
that a powerful electric current is interrupted, the terminals
being large carbon rods, and the space between having been
filled with a mixture of alumina, carbon, and the metal to be
HISTORY OF ALUMINIUM. 29
alloyed, the intense heat generated in contact with this mixture
causes the metal to melt and the alumina to be reduced to alu-
minium, which combines with the metal, while the oxygen
escapes as carbonic oxide.
It is interesting to note as separating the Cowles, as well as
the Heroult, process from the previously-mentioned electrolytic
methods, that while the latter produce almost exclusively pure
aluminium in their electric operation, finding it inexpedient, if
not perhaps impossible, to add other metals and form alloys at
once — the former experience almost the reverse of these condi-
tions, and as yet are confined exclusively to the direct produc-
tion of the alloys.
The Heroult process was first put in practical operation on
July 30th, 1888, at the works of the Swiss Metallurgic Com-
pany (Societe Metallurgique Suisse), at Neuhausen, near
Schaffhausen. The patents for the process were granted in
France and England in April and May, 1887, and in the United
States in August, 1888. The company named above is com-
posed of some of the largest metal-workers in Switzerland.
Previously to their adoption of this process they had experi-
mented with Dr. Kleiner's electrolytic method, but abandoned
it, and on becoming the owners of the Heroult process imme
diately started it up practically on a large scale, and with signal
success.
The process consists in electrolyzing molten alumina which
has been rendered fluid by the heat of the arc, using as the
positive anode a large prism of hard carbon and as the negative
a substratum of molten copper or iron, the arrangement of the
parts being such that the process seems to proceed, when once
well under way, in all respects as tlfe simple electrolysis of a
liquid. Using water power for driving the dynamos, the
economical production of alloyed aluminium at 4.5 francs per
kilo (50 cents per pound), was an assured fact.
The success of this process at Neuhausen was so marked as
to attract general attention, and in the latter months of 1 888
several large German corporations, prominent among which was
30 ALUMINIUM.
the Allgemeine Electricitats Gesellschaft of Berlin, sent repre-
sentatives to arrange for the purchase of the Heroult patents
for Germany. The outcome of these examinations and negotia-
tions was the purchase by this German Syndicate of HerouU's
continental patents and the founding by them and the former
Swiss owners of the Aluminium Industrie Actien-Gesellschaft,
with a capital of 10,000,000 francs. In December, 1888, the
new company took possession at Neuhausen, and commenced
the construction of a plant many times larger than the original
one, their plans also including the erection of foundries and
mills for casting and manufacturing their alloys. Dr. Kiliani,
the well-known writer on electro-metallurgical subjects, was
working manager for the company.* The new plant utilized
3000 horse power, and had a capacity of 3000 pounds of alloyed
aluminium daily.
In the same year, the Societe Electro-Metallurgique Fran-
caise established a works at Froges (Isere) 12 miles from
Grenoble, to work the Heroult process, with Kiliani's modifica-
tions. They used 400 horse-power, which later was enlarged
to 800, and in 1894 acquired a large water power at La Praz,
near Modane, where works have been erected and lately put
into operation.
The process now used here and in Switzerland is not the
original Heroult process as previously described. Dr. Kiliani
introduced some modifications in the apparatus, but no pure '
aluminum was made by either of the Heroult works until the
end of 1889, when there was begun the use of cryolite in the
furnace to reduce the melting point of the alumina and the
electrical tension required to operate it. As thus modified, the
process is essentially identical in principle with Hall's process ;
in fact, the U. S. Patent office refused Heroult's application for
a patent on account of Hall's priority to the process. An at-
tempt was made in 1889 to work the Heroult alloy process in
the United States, an experimental plant being started at
* Dr. Kiliani died suddenly in January, 1895, in the midst of his duties.
HISTORY OF ALUMINIUM. 3 1
Bridgeport, Conn., in August of that year, but it was stopped
by the burning out of the dynamo. In 1890 another dynamo
arrived from the Oerlikon works, at Zurich, and the process
was operated for some time on an experimental scale at Boon-
ton, N. J., but was abandoned in 1891.
During the years 1885 to 1890 both the Cowles and Heroult
alloy processes were successful in producing aluminium in al-
loys at a lower cost than the market price of pure aluminium,
and therefore built up a considerable business. Since pure
aluminium has reached so low a price, metal mixers prefer to
make their own alloys from the pure metal, and the ready-made
alloys have lost their market.
The Alliance Aluminium Company of London, England, was
organized in the early part of 1888, with a nominal capital of
^500,000. This company owned the English, German, French,
and Belgian patents of Prof. Netto, of Dresden, for the manu-
facture of sodium and potassium and the reduction of cryolite
thereby ; the patents of Mr. Cunningham for methods of reduc-
tion of the same metals ; and methods devised by Prof. Netto
and Dr. Saloman, of Essen, for producing aluminium of great
purity on a commercial scale. The two latter named gentle-
men are said to have invented their processes after long ex-
perimenting at Krupp's works at Essen; and, since the ap-
paratus used was mounted on trunnions, many rumors were
spread by the newspapers that aluminum was being made (by
tons, of course) in a Bessemer converter by Krupp, of Essen.
Prof. Netto reduced sodium by a continuous process, by allow-
ing fused caustic soda to trickle over incandescent charcoal in a
vertical retort, the apparatus containing many ingenious details
and giving promise of being quite economical. One method of
using the sodium in reduction consisted in the use of a plunger
to which bars of sodium were attached and held at the bottom
of a crucible full of molten cryolite ; another depended on the
use of a revolving cylinder in which the cryolite and sodium
reacted, and appears more chimerical than Netto's other pro-
positions. This latter device, however, is said to have been
operated at Essen.
32 ALUMINIUM.
In June, 1888, the Alliance Company were located at King's
Head Yard, London, E. C, and several small reduction furnaces
were being operated, each producing about 50 lbs. of alumin-
ium a day, estimates of the cost at which it was made giving
6 to 8 shillings per pound. In the early part of 1889 the
" Alkali Reduction Syndicate, Limited," leased ground at Hep-
burn on which to erect works for making sodium by Cunning-
ham's patents, the sodium produced being sent to Wallsend,
near Newcastle-on-Tyne, where the Alliance Company's reduc-
tion works were located.
In 1890 this company could not profitably compete with the
electrolytic processes, and in 1 892 their works were sold at auc-
tion.
Ludwig Grabau, of Hanover, Germany, has made several
patented improvements in producing aluminium, which are in
the same direction as Prof. Netto's methods. Mr. Grabau be-
lieves that in order that aluminium may possess its most valuable
qualities, either for use alone or in alloying, it should be of
almost chemical purity, and as the best means of attaining this
end economically he has improved the sodium method on
these three lines : —
1st. Production of cheap pure aluminium fluoride.
2d. Production of cheap sodium.
3d. Reduction in such a manner that no possible impurities
can enter the reduced metal, and that the sodium is completely
utilized.
Mr. Grabau has devised processes for making pure alumin-
ium fluoride from kaolin, sodium by electrolysis of fused salt,
and has succeeded in producing some very pure aluminium,
but not cheaply enough to compete with the Hall and Heroult
processes.
Col. William Frishmuth, of Philadelphia, operated a small
chemical works, and before i860 made sodium by Deville's
process, and with it made aluminium in small quantities. He
claimed to have other methods of producing aluminium cheaply,
but none of them were practicable. He deserves credit for hav-
HISTORY OF ALUMINIUM. 33
ing made a good casting of the aluminium tip on tlie Wasiiing-
ing Monument at our national capital.
In 1889 the aluminium industry was finely represented at the
Paris Exposition. It was the period in which the sodium pro-
cesses were at their culmination, and the electrical processes
just becoming serious competitors. A detailed account of the
exhibits reads as follows :
Societe Anonyme pour I'lndustrie de 1' Aluminium : In a
large case, the frame of which was aluminium bronze, samples
of aluminium, ferro-aluminium, aluminium bronze, forged and
rolled, and numerous articles of the latter alloy. Cowles Elec-
tric Smelting and Aluminium Company : Samples of ferro-alu-
uminium, aluminium bronze and aluminium brass of various
grades, aluminium silver, and numerous useful articles made of
these alloys. Brin Bros. : Samples of aluminium with thin iron
and steel castings made by its use. The Alliance Aluminium
Company:. Two large blocks of aluminium, cast hollow, weigh-
ing possibly 1,000 pounds and 500 pounds, respectively. The
inclosing balustrade and decorations were principally of alu-
minium or aluminium bronze. The Aluminium Company,
Limited : A solid casting of aluminium bronze weighing y^ ton,
and on this a solid block of 98 per cent, aluminium weighing
the same. In the corners of the case piles of ingots of 99 per
cent, aluminium, 10 per cent, bronze, 5 per cent, bronze, 10
per cent, ferro-aluminium, and 20 per cent, aluminium steel.
Besides which were a 7-inch bell, springs, statues, aluminium
plate, round and square tubes, wire, sheet, etc. Such were the
aluminium exhibits, which attracted as much interest as the
historic ingot of 1855 did at its debut, and, not taking into ac-
count that Mr. Hall's process was not represented and that the
German makers were debarred from exhibiting because of in-
ternational pique, yet the exhibit shown was one which demon-
strated the great advances made in the previous five years.
Since 1 890, the progress of the aluminium industry has been
steady but sure. The sodium processes have dropped alto-
gether from the race, and the electrical processes occupy the
3
34 ALUMINIUM.
field. Among these, the processes producing alloys only have
dropped out of sight. Among those that remain, only those
favorably situated, near abundant water power and with cheap
supplies of alumina, have flourished. The industry has reached
a strict commercial basis, in which every cent of cost has to be
considered, and every item of expense reduced to a minimum.
In 1890 the Cowles Electric Smelting and Aluminium Com-
pany began selling pure aluminium. They were sued by the
Pittsburgh Reduction Company for infringement of the Hall
patents, and in the early part of 1893 were enjoined by the
courts from continuing their pure-metal process, it being de-
clared an infringement of Hall's patents.
Mention should be made of the aluminium exhibit at the
Columbian Exposition in Chicago, 1893. The only makers
represented were the Pittsburgh Reduction Company, but their
exhibit was a very satisfactory representation of the state of the
art. A working model of an extraction pot was shown, hun-
dreds of pounds of the metal in all shapes and worked in every
way, a fine set of aluminium alloys, and several cases of manu-
factured goods made from their metal by various American
firms. Mr. Hirsh of Chicago showed aluminium electroplated
on other metals and on wood. The writer exhibited a metal-
lurgical suite showing the minerals from which aluminium is
extracted, samples of aluminium made by the various processes
which have been used, samples showing the physical properties
of the metal, its working, soldering, etc., and a large number of
its alloys.
The statistics about to be given will show graphically the
story of the rise of the aluminium industry. The last ten years
have witnessed an undreamt-of progress. Hereafter the lower-
ing in price can only be counted at a few cents a pound, but
the increase of production may be noted in thousands of tons.
A most fitting ending to this historical sketch would be simply
to repeat what I wrote three years ago, viz., " The nineteenth
century will live in history as that century which gave to the
world the railway, the telegraph, the telephone, the dynamo,
Bessemer steel and aluminium."
HISTORY OF ALUMINIUM. 35
STATISTICAL.
The following table shows the price at which aluminium has
been sold since it was first placed on the market :
Dale. Place. Per kilo. Per pound.
1856 (Spring) Paris looo fr. ^90.90
1856 (August) " 300 " 27.27
1859 " 200" 17-27
1862 " 130" 11.75
1862 Newcastle ii-75
1878 Paris 130" 11.75
1886 " 12.00
1887 Bremen 8.00
1888 London 4.84
1889 Pittsburgh 2.00
1891 " 1 1.50
1892 " i.oo
1893 " 0-75
1894 " 0.50
1895 Switzerland 3 M. 0.35
Until 1885 the selling price of aluminium bronze depended
directly on the price of aluminium, being about $1.50 per
pound for the ten' per cent, alloy. With the advent of the
Cowles and, later, the Heroult alloy-processes, the price fell
below what the contained aluminium would have cost, as is
shown by the selling price of the ten per cent, bronze, as fol-
lows:
Date. Place. Per kilo. Per pound.
1878 Paris 18.00 fr. gi.64
1885 Cowles Bros 4.50 " 0.40
1888 " " 3-85 " 0.35
1888 Heroult process, Neuhausen 3.30 " 0.30
Since 1889 the cost of the bronze has again been dependent
on the cost of the pure metal, so that no separate figures are
necessary, With copper at $0.10 per pound, and aluminium
at $0.50, the cost of 10 per cent, bronze is not over $0.20 per
pound.
As to the amount of aluminium which has been produced.
36 ALUMINIUM.
we can make the following estimates, gleaned from various
sources :
France.
Kilos.
1854-56 Deville 25
1859 Nanterre (Deville) 720
1859 Rouen (Tissier Bros.) 960
1865 France 1,090
1869 " 455
1872 Sallndres (H. Merle & Co.) 1,800
1882 " " " 2,350
1884 " " " 2,400
1887 France 3,500
1888 " 4,500
1889 " 14,840
1890 " 37,°oo
1891 " 36,000
1892 " 40,000
A careful estimate of the total amount made in France by
the Deville process, from 1855 to 1888, places it at 43,000
kilos. Since 1888, there has been made by other processes
128,000 kilos up to the year 1893, making a total of 171,000
kilos, or 375,000 pounds.
England.
Pounds.
1872 Bell Bros 1,650
1889 Castner process 50,000
1891 Electrolytic processes 90,000
1892 " " 90,000
The total English production up to 1890 was probably not
over 70,000 pounds. The Castner process produced altogether
from July, 1888 to 1891, 250,000 pounds. The total produced
in England to the end of 1 892 is therefore in the neighborhood
of 450,000 pounds.
Switzerland.
Kilos.
1890 Neuhausen 40,540
1891 " 168,670
1892 " 300,000
1893 " 480,000
1894 •' 600,000
HISTORY OF ALUMINIUM. 37
The total production of these works to the end of 1894 was
over 1,500,000 kilos, or 3,300,000 pounds.
United States.
Pounds.
1883 Frishmuth 70
1884 " 125
1885 " 230
1885 Cowles Bros, (in alloys) 450
'886 " " 6,500
•887 " " 17,800
1888 Pure and alloyed 19,000
1889 " 47,468
1890 " 61,281
1891 " 150,000
1892 " 259,885
1893 " • 333,629
1894 '• 706,000
World's Production to End of 1892.
Kilos. Pounds.
France 171,000 376,000
England 204,500 450,000
Switzerland 500,000 1,100,000
Germany (1885- 1 889) 50,000 110,000
United States 250,000 550,000
Total 1,175,500 2,586,000
The amount made in 1 893 was as follows :
France (estimated) 40,000 kilos.
Switzerland 480,000 "
United States 150,000 "
Total 670,000 " =: 1,474,000 pounds.
An estimate for 1 894 would be as follows :
France 100,000 kilos.
Switzerland 600,000 "
United States 320,000 "
Total 1,020,000 " = 2,244,000 pounds.
The total amount of aluminium made from 1855 to the be-
38 ALUMINIUM.
ginning of 1895 is, therefore, in the neighborhood of 2,865,500
kilos, or 6,304,000 pounds, while the annual production has
reached 1,000 long tons, and will probably be increased during
1895 to nearly 2,000 tons.
In comparing these figures with the production of other
metals, it is important to bear in mind the low specific gravity
of aluminium. For most practical applications, the bulk of the
metal used is a fixed quantity, and 1,000 tons of aluminium
are equal in volume to
4,600 tons of lead.
4,000 " " silver.
3,500 " " nickel.
3,300 " " copper.
2,800 " " tin.
2,700 " " zinc.
CHAPTER II.
OCCURRENCE OF ALUMINIUM IN NATURE.
There is no other useful metal, iron not excepted, which
is so widely scattered over the earth and occurs in such
abundance. F. W. Clarke of the Smithsonian Institution has
calculated that the percentage of aluminium in the earth's crust,
as far as it is known to us, is 7.81, while that of iron, the next
most abundant element, is 5.46.
Aluminium is not found metallic. Stocker * made the state-
ment that aluminium occurred as shining scales in an alumina
formation at St. Austel, near Cornwall, but he was in error.
But the combinations of aluminium with oxygen, the alkalies,
fluorine, silicon, and the acids, etc., are so numerous and occur
so abundantly as not only to form mountain masses, but to be
also the bases of soils and clays. Especially numerous are the
combinations with silicon and other bases, which, in the form
of feldspar and mica, mixed with quartz, form granite.
These combinations, by the influence of the atmospheric air
and water, are decomposed, the alkali is replaced or carried
away, and the residues form clays. The clays form soils, and
thus the surface of the earth becomes porous to water and
fruitful. It is a curious fact that aluminium is rarely found in
animals or plants. According to Church, f alumina is found
only in a few vascular cryptogamous plants, whose ash con-
tains up to 20 per cent.
Ricciardi concluded from numerous experiments that the
assimilation of alumina by plants does not depend upon the
abundance of alumina in the soil, and that, generally speaking,
* Joum. fr. prakt. Chem., 66, 470.
t Proc. Royal Society, Vol. 44, p. 121.
(39)
40 ALUMINIUM.
there is more found in the trunk and branches, less in the
husks and seeds, and least in the leaves.
Most of the aluminium compounds appear dull and disagree-
able, such as feldspar, mica, pigments, gneiss, amphibole, por-
phyry, eurite, trachyte, etc. ; yet there are others possessing
extraordinary lustre, and so beautiful as to be classed as prec-
ious stones. Some of these, with their formulae, are :
Ruby AI2O3
Sapphire Al^Oj
Garnet (Ca.Mg.Fe.Mn)3Al2Si30,2
Cyanite AUSiOj
Some other compounds occurring frequently are :
Turquoise AljPPs.HjAljOs.aHjO
Lazulite (MgFe)AljP203 -|- Aq
Wavellite 2AI2P2O8.H1.AI2O6.9H2O
Topaz 5AL,Si05.Al,SiFi„
Cryolite Al^Fg.eNaF
Diaspore AIJO3.H2O
Bauxite AI2O3.2H2O
Aluminite AlaSOe.gH^O
Alunite K^s6i.Al^Sfi,^.2H^Alfii
Soda Feldspar NajAl2Si60ig
Potash Feldspar KjAljSigOjj
Lime Feldspar CaAljSijOg
Kaolin Al2SijO,.2H20
Bauxite and cryolite are the minerals most used for produc-
ing aluminium, and their preference lies mainly in their purity.
Native alums generally occur in out of-the-way places and not
in beds of very large extent.
Bauxite.
Bauxite is a hydrous aluminium oxide of variable composi-
tion, sometimes approaching diaspore in its proportion of water,
but with the aluminium always more or less replaced by iron,
and some silica disseminated through it. Its color is creamy
white when free from iron, and its structure usually pisolitic,
that is, in small globules like peas. It was first found in
OCCURRENCE OF ALUMINIUM IN NATURE. 4 1
France, near the town of Baux, large deposits occurring in
the departments of Var and Bouches du Rhon, extending from
Tarascon to Antibes. Several of these beds are a dozen yards
thick, and sixteen kilometers in length. Deposits are also
found in the departments of I'Herault and I'Arriege. Very im-
portant beds are found in Styria, at Wochein, and at Freis-
stritz, in Austria, a newly discovered locality where the mineral
is called Wocheinite. Here it has a dense, earthy structure,
while that of France is conglomerate or oolitic. Deposits
similar to those of France are found in Ireland at Irish Hill,
Straid, and Glenravel. Further deposits are found in Hadamar
in Hesse, at Klein Steinheim, Langsdorff, and in French
Guiana.
In the United States large beds have been found in Alabama,
Georgia, and Arkansas. Those of Georgia have been worked
since 1890, and are now affording a large part of all the
bauxite consumed in this country. The deposits of the Coosa
Valley in Georgia and Alabama are worked by three com-
panies, the Republic Mining and Manufacturing Company, the
Georgia Bauxite and Mining Company, and the Southern
Bauxite Mining and Manufacturing Company. These three
companies produced, in 1893,9,200 tons, which was three-fifths
of the total bauxite consumed in the United States, the rest
being imported from Ireland. The ore is found in beds or
pockets, and while the quantity in sight is not inexhaustible,
yet there is sufficient for many years to come, at the pres-
ent rate of mining. These bauxites are as pure as those
of Europe, and the manufacturers using them say they are
more easily worked and so prefer them to the imported, even
though they often carry less alumina and cost more. The
Arkansas ore occurs in tertiary formations, in irregular de-
posits of 5 to 40 feet in thickness, not over 300 feet above tide
water. H. L. Fletcher, of Little Rock, owns much of the land
on which they occur.
The cost of imported bauxite is $5 to $7 a ton ; of Ameri-
can bauxite $5 to 12 per long ton, according to where the
42
ALUMINIUM.
market is; best selected Georgia bauxite brings $io per ton
in New York city.
The following are analyses of foreign bauxites ; besides the
ingredients given there are also traces of lime, magnesia, sul-
phuric, phosphoric, titanic and vanadic acids.
Alumina ■ • ■
Ferric oxide
Silica
Alkalies. • . .
Water
60.0
25.0
3-°
12.0
75.0
12.0
i.o
12.0
3
4
63.16
72.87
23-SS
13-49
4.15
4.25
0.79
0.78
8-34
8.50
44.4
30-3
15.0
9-7
6
54.1
10.4
12.0
29.9
Alumina ■ ■ .
Ferric oxide
Silica
Alkalies . ■ -
Water
Alumina • • •
Ferric oxide
Silica
Alkalies
Water
7
64.6
8
9
48.12
10
II
61.89
29.80
43-44
2.0
3.67
2.36
2.1 1
1.96
7-5
44.76
7-95
'5-°5
6.01
24.7
13-86
40-33
35-7°
27.82
13
SS-6I
7.17
4.41
32-33
14
76.3
6.2
1 1.0
26.4
15
50.85
14.36
5.14
0.26
28.38
16
49.02
12.90
10.27
0.31
25-91
45-76
18.96
6.4 1
0.38
27.61
73.00
4.26
2.15
18.66
Index: —
I and 2. From Baux (Deville).
Dark \
T ■ vj ]■ Wocheinite (Drechsler).
Red brown \
Yellow >■ Bauxite from Freisstritz (Schnitzer).
White >
White Wocheinite (L. Mayer and O. Wagner).
Bauxite from Irish Hill.
OCCURRENCE OF ALUMINIUM IN NATURE.
43
10. Bauxite from Co. Antrim (Spruce).
11. « " Glenravel (F. Hodges).
12 and 13. " " Hadamar in Hesse (Retzlaff).
14. From Klein-Steinheim (Bischof).
15 and 16. From Langsdorfi (I. Lang).
17. Bauxite from Dublin, Ireland, brought to the Laurel Hill Chemical
Works, Brooklyn, L. I., and there used for making alums. It is dirty
white, hard, dense, compact, and in addition to the ingredients given
above contains 0.59 per cent, of lime and some titanic acid. It costs
$6 per ton laid down in the works. The above analysis, made by Mr.
Joiiet, is furnished me by the kindness of the superintendent of the
works, Mr. Herreshoff.
The American bauxites are fully equal to the foreign in
quality, as is shown by the following analyses :
Ferric Oxide.
Silica
Water
Titanic Acid.
18
Alumina | 37-62
1.83
11.48
28.63
19
55-59
6.08
10.13
28.99
20
21
22
46.44
58-60
46.72
22.15
9.II
2.14
4-89
3-34
29.01
26.68
28.63
20.15
—
—
0.87
Alumina —
Ferric Oxide
Silica
Water
Titanic Acid
58.61
2.63
8.29
27.42
3-15
24
67-53
trace
1-34
28.00
2.92
25
60.61
0.21
2-47
32.00
4.18
26
61.87
2.38
0.40
30.50
27
40-93
22.60
8-99
20.43
18. Little Rock Region, Pulaski Co., Arkansas.
jg >I « " " "
20. Red variety. Saline Co., Arkansas.
21. Pink "
22. White variety, Floyd Co., Georgia.
2j-
24. Georgia Bauxite Company.
2c " " "
26. Wharwhoop Mine, Cherokee Co., Alabama.
27. Red variety, Cherokee Co., Alabama.
44 ALUMINIUM.
Regarding French bauxites, Francis Laur, the first to work
the French deposits, states* that one of their peculiarities is
that the bulk of that mined contains a nearly constant amount
of alumina, of silica, ferric oxide and water taken together, and
of other impurities. The proportions are very nearly
Alumina 68 to 70 per cent.
Silica, ferric oxide and water 27 "
Other impurities 3 to 4 "
In the bauxite from Baux, that first worked, the silica, ferric
oxide and water are present in about equal proportions ; that
is, about 8 to 10 per cent, of each. In the pale bauxite from
Villeveyrac (Herault) there is almost no iron, and the 27 per
cent, is nearly evenly divided between silica and water ; what
small amount of ferric oxide does occur in it can be put into
the list of " other impurities." The red bauxite, discovered in
1880 in the south of France, is very constant in composition,
and may be regarded as the inverse of the pale variety. In this
red kind the silica is so small as to be relegated to the acces-
sory constituents, while water and ferric oxide alone make up
the 27 per cent. These three varieties represent the three types
of bauxite which are mined in large quantities. The pale
variety, being low in iron, is preferred for making aluminium
sulphate by treatment with sulphuric acid, which attacks it very
readily; the red kind is preferred for the sodium carbonate
treatment, as the iron does not interfere, while silica is kept out
of the alumina produced. Besides these kinds, some varieties
are found with the 27 per cent, either all water, all silica or all
ferric oxide. We would thus have, as the composition of the
typical kinds of bauxite found in France, the following:
Water. Silica. Ferric oxide.
Hyaline bauxite 27 o o
Silicious type, compact o 27 o
Ferruginous type, in pisolites o o 27
Red bauxite of Var 131^ o 131^
Pale bauxite of Villeveyrac 131^ i^}4 o
Mixed bauxite of Baux 9 9 9
* Trans. Am. Inst. Mining Eng., Feb., 1894.
OCCURRENCE OF ALUMINIUM IN NATURE. 45
Mr. A. E. Hunt, of Pittsburgh, in the discussion of this paper,
remarked that there are vast quantities of bauxite in Georgia,
Alabama and Arkansas, which run low in both silica and ferric
oxide, containing less than 5 per cent, of both these ingredients,
but with about 4.5 per cent, of titanic acid. It is his experience
that when the water of hydration is below 31 per cent., in the
greyish and white bauxite from Georgia and Alabama, the
silica is always high. If the bauxite is red, however, the water
may be low without the silica being high. He cites the follow-
ing analyses illustrating this point :
Combined water.
Silica.
Ferric oxide.
Titanic acid.
Alumina,
33-43
0.80
0.47
4.20
61.10
32.00
2.66
0.47
4.06
60.81
20.93
22.96
0.47
4.72
51.14
16.70
32-03
0.71
3-76
47-03
18.20
3.10
17-3°
3-9°
57.00
It will be seen that Mr. Laur's generalizations regarding
French bauxites do not hold good for the American varie-
ties ; the constancy of the titanic aci,d is also remarkable.
Cryolite.
Cryolite was first found at Ivigtuk in Arksut-fiord, west coast
of Greenland, where it constitutes a large bed or vein in gneiss.
It was very rare even in mineralogical collections until 1855,
when several tons were carried to Copenhagen and sold under
the name of " soda mineral." It is a semi-transparent, snow-
white mineral. When impure it is yellowish or reddish, even
sometimes almost black. It is shining, sp. gr. 2.95, and hard-
ness 2.5 to 3. It is brittle, not infrequently contains ferrous
carbonate, sulphide of lead, silica, and sometimes columbite.
It is fusible in the flame of a candle, and on treatment with
sulphuric acid yields hydrofluoric acid. As will be seen further
on, cryolite was first used by the soap-makers for its soda ; it
is still used for making soda and alumina salts, and to make a
white glass which is a very good imitation of porcelain. The
Pennsylvania Salt Company in Philadelphia import it from
4-6 ALUMINIUM.
Ivigtuk by the ship-load for these purposes ; lately they have
discontinued making the glass. Cryolite is in general use as a
flux. A very complete description of the deposit at Ivigtuk
can be found in Hoffman's " Chemische Industrie."
Pure cryolite contains
Aluminium l3-°
Fluorine 54-5
Sodium 32.5
100.00
Or otherwise stated,
Aluminium fluoride 40.25
Sodium fluoride ■* 59-75
100.00
From the reports in the Mineral Resources of the United
States we find that there was imported by the Pennsylvania
Salt Company in 1892, 8000 long tons, which was valued at
$9 a ton. The importers say this value is too low ; they sell
what they call pure prepared cryolite at $60 a ton. This so
called pure article was found by Prof. Rogers, of Milwaukee, to
contain two per cent, of silica and one per cent, of iron ; in
fact, the whitest cryolite always contains silica microscopically
disseminated through it, which cannot be separated out by any
means.
The only known deposit of cryolite in the United States is
that found near Pike's Peak, Colorado, and described by W.
Cross and W. F. Hillebrand in the "American Journal of
Science," October, 1883. It is purely of mineralogical import-
ance and interest, occurring in small masses as a subordinate
constituent in certain quartz and feldspar veins in a country
rock of coarse reddish granite. In composition, however, it is
practically identical with the Greenland cryolite, so that the
following analysis by Mr. Hillebrand will stand for a typical
analysis of cryolite as found in nature :
OCCURRENCE OF ALUMINIUM IN NATURE. 47
Fluorine 53.55 per cent.
Aluminium , 12,81 "
Sodium 32.40 "
Ferric Oxide 0.40 "
Lime 0.28 "
Water 0.30 "
Corundum.
Until 1869 the sole sources of corundum were a few river
washings in India and elsewhere, where it was found in scat-
tered crystals. Its cost was twelve to twenty-five cents a
pound. Within the last twenty years numerous mines have
been opened in the eastern United States, the first discovery of
which was due to Mr. W. P. Thompson, and is thus described
by him : *
" In 1869, in riding over a spur of the Alleghenies in north-
ern Georgia, I found what has proven to be an almost inex-
haustible mine of corundum in the chrysolite serpentine, the first
instance on record of the mineral being found. /« situ. Previ-
ously it had been washed out of debris at Cripp's Hill, N. C,
and at a mine in West Chester, Pa., both on the slopes of the
chrysolite serpentine. The clue being thus obtained accident-
ally, about thirty mines were shortly afterwards discovered in
the same formation ; but of the thousands of tons thus far dug
out, the larger portion has come from the mines I discovered.
" At present it can be bought at about ten dollars per ton at
the mines. It is nearly pure alumina. Disapore, a hydrated
alumina, is also found in the same region and locality. Corun-
dum will probably always be the principal source in America
of material from which to manufacture pure aluminium ; but in
Great Britain, in all probability, manufacturers must look to
alumina prepared artificially from cryolite or from sulphate of
alumina."
In 1892 the production of corundum in the United States
was somewhat over 2000 short tons, valued at $40 a ton when
sifted and broken to proper sizes for the market, the Hamp-
* Journal of the Society of Chemical Induustry, April, 1886.
48 ALUMINIUM.
den Emery Company, at Laurel Creek, Ga., and at Corundum
Hill, N. C, and the Unionville Corundum Mines Company, at
Unionville, Chester Co., Pa., being the principal producers.
Thus, while corundum may be worth in bulk at the mines only
$io a ton, yet it is extremely hard to crush, and when broken
up fine is worth far more as an abrasive than as an aluminium
ore. The present large development of bauxite mining has
completely nullified the use of corundum as a source of alumin-
ium, and I do not suppose that at present a single pound of
aluminium is being made from it.
Kaolin.
The mineral kaolin is variously known as white china clay,
fuller's- earth, or pure white clay. It is essentially a hydrated
silicate of aluminium, containing when pure
Alumina 39.8 per cent.
Silica 46.3
Water 13.9 "
Its chemical formula is Al2O3.2SiO2.2H2O. If the water is
driven off by calcination, the residue contains 46.2 per cent.
of alumina, or 24.4 per cent, of aluminium.
Kaolin has been formed mostly by the atmospheric decom-
position of feldspar, the alkalies of which are changed into
carbonates by the carbonic acid of the rain water, and are then
leached out, carrying with them part of the silica in solution,
and leaving kaolin, according to the reaction,
K2Al2Si60,6f2H20+C02=Al2SiA.2H20+K2C03-t-4Si02.
Kaolin acquires a certain plasticity when mixed with water.
Hydrochloric and nitric acids have no action on it, but cold
sulphuric acid dissolves its alumina, setting the silica at liberty.
It is infusible unless contaminated with particles of feldspar or
calcium sulphate, carbonate, or phosphate. The specific gravity
of kaolin is 2.3. If fused with six times its weight of caustic
potash, the resulting mass gives up potassium aluminate when
OCCURRENCE OF ALUMINIUM IN NATURE. 49
washed with water, An analogous result is obtained with
sodium carbonate. Grabau has prepared very pure aluminium
fluoride from kaolin by the use of sulphuric acid and subse-
quent boiling with fluorspar.
Large deposits of kaolin are found in many parts of the
world. The best locality in Europe is near Limoges, France,
with which the famous Sevres porcelain is made. Large beds
are found in Cornwall and West Devon, England. In the
United States the largest deposits are at Wilmington, Del., and
in South Carolina, Georgia and Alabama. These deposits are
worked extensively, and the product used by the pottery,
paper, cotton, and various other industries. The value at the
mines is very small, it not costing over $0.50 per ton to mine
it, but for many purposes it must be crushed, washed, and even
floated, which increases its value to $5 or $10 a ton in New
York city.
The purity of kaolin, and the almost inexhaustible beds in
which it occurs, stamp it as the natural ore of aluminium. All
that is needed is a cheap process for separating the pure alu-
mina from the silica, in which case no other mineral could
compete with it as the main staple of the aluminium industry.
This is a promising field for chemical experimenters, for such
a process would be of great value.
Common clays are either very impure kaolin, or else they
contain chemically a much larger proportion of silica. The
percentage of silica may range from 50 per cent, up to 70 per
cent, while that of the alumina present ranges downwards from
35 to 15 per cent. These common clays are far too impure
and low in silica to serve as a source of aluminium, and in no
case could they compete with kaolin.
Some anhydrous silicates of aluminium are found in nature,
such as Disthene, Andalusite and Cyanite, whose formula is
AUOj.SiOj, containing 62.5 per cent, of alumina ; but they do
not occur in large quantities, and, even if they did, are so hard
and difficult to decompose that they would never be preferred
to kaolin.
4
50 aluminium.
Native Sulphate of Alumina.
In the summer of 1884, a large deposit of rock called " native
alum" was discovered on the Gila River, Socorro County, New
Mexico, about two miles below the fork of the Little Gila, and
four miles below the Gila Hot Springs. The deposit is said to
extend over an area one mile square and to be very thick in
places. The greater part of the mineral is impure, as is usual
with native occurrences, but it is thought that large quantities
are available. A company formed in Socorro has taken up the
alum-bearing ground. Through the kindness of Mr. W. B.
Spear, of Philadelphia, the author was enabled to get a speci-
men of the mineral.
It is white, with a yellowish tinge. On close examination it
is seen to consist of layers of white, pure-looking material ar-
ranged with a fibrous appearance at right angles to the lamina-
tion. These layers are about one-quarter of an inch thick.
Separating them are thin layers of a material which is deeper
yellow, harder and more compact. The whole lump breaks
easily, and has a strong alum taste. On investigation, the
fibrous material was found to be hydrated sulphate of alumina,
the harder material sulphate of lime. Analysis showed 7 to 8
per cent, of insoluble material, the remainder corresponding to
the formula Al2(S04)3.i8H20. A small amount of iron was
present.
State Geologist Waring informs the writer that the deposits
occur only in sheltered spots protected from the rain, that the
region is eruptive, and that where the trachyte rock is being
decomposed by sulphuric gases and waters, the salts rise to the
surface and form crusts in protected places. Often the earth
contains 10 per cent, or more of the anhydrous sulphate.
A similar mineral occurs in Purgatory Valley, 12 miles east of
Trinidad, Colorado.
A variety of the same mineral containing some silica was
found in a stratum 25 feet thick by the Congo Coal Company,
while sinking a shaft at Congo, Ohio, in 1893. An analysis of
this by Dr. Lisle, of Springfield, Ohio, gave
OCCURRENCE OF ALUMINIUM IN NATURE. Si
Alumina 50.16 per cent.
Silica 28.98 "
Lime 0.46 "
Sulphuric acid 16.21 "
Water 4.28 "
These minerals would appear to ofifer a cheap source of
alumina, as the operations necessary for treating them are very-
simple, being solution in warm water, filtration, evaporation,
and roasting. The excessive freight charges are against the
New Mexico and Colorado deposits, but that in Ohio should
be of considerable economic importance if the reports concern-
ing its extent are verified.
CHAPTER III.
PHYSICAL PROPERTIES OF ALUMINIUM.
Commercial aluminium is never chemically pure, and there-
fore displays properties varying more or less from those of the
pure .metal according to the character and amount of impurities
present. In this treatise, whenever the properties of aluminium
are mentioned, they must be understood to refer to the chemi-
cally pure metal, and not to the commercial article, unless spe-
cifically stated.
The impurities most frequently present in commercial alu-
minium are iron and silicon. These are found in all brands,
varying in amount from i per cent, in the purest to 6 and even
8 per cent, in the worst. Besides these, various other impuri-
ties are found coming from accidental sources in the manufac-
ture ; thus, some of the first metal made by Deville contained
a large amount of copper (Analysis i), coming from boats of
that metal which he used in his experiments. Metal made
later by Deville contained zinc, coming from zinc muffles which
he had borrowed and used for retorts, old retorts broken up
having been used in the composition of the new ones. More
recently, aluminium has been produced by the agency of
sodium in the presence of lead, which latter it takes up in small
amount. Sodium is liable to remain alloyed in very small pro-
portion, yet it is an element so easily attacked that it destroys
some of the most valuable qualities of the aluminium. The
distinct effect, however, of each of these usual impurities in
modifying the physical properties of aluminium has not yet
been investigated in a thoroughly satisfactory manner. A few
years more, however, of increasing familiarity with and hand-
ling of the metal on a large commercial scale will, I believe,
(52)
PHYSICAL PROPERTIES OF ALUMINIUM. S3
cause the effect of foreign elements on aluminium to be as
plainly recognized as is now the case with carbon and the
metalloids in iron. In general, we may say that silicon seems
to play a role in aluminium closely analogous to that of carbon
in iron ; the purest aluminium is fibrous and tough, but a small
percentage of silicon makes it crystalline and brittle. Further-
more, a considerable proportion occurs in the graphitoidal
state, and may be separately estimated as graphitoidal silicon
by dissolving the metal in dilute hydrochloric acid in the pres-
ence of bromine water. A small amount of silicon, however,,
gives pure aluminium a bluish cast, a disagreeable smell, and
greatly lessens its resistance to corroding agents. A small
proportion of iron makes the metal denser and stronger, but a
quantity above i per cent, quickly makes it brittle. A small
quantity of copper whitens aluminium, makes it much stronger
and lessens its shrinkage in casting, but with over 5 per cent,
it becomes brittle.
As aluminium was made by the sodium processes, it con-
tained as impurity about equal quantities of iron and silicon ; as
made by the electrolytic processes, the iron present is usually
much less than the silicon. Carbon can only exist in alumin-
ium that has been subjected to an intense heat, such as in an
electric furnace, when it may be absorbed in small quantity,
and makes the metal brittle ; it does not occur, however, in
ordinary commercial aluminium. Titanium may occur in
aluminium made from raw bauxite, which frequently contains
titanic oxide ; its presence in small amount makes the metal
much stronger, but gives it a bluish tint. There is needed a
systematic investigation of the effect of small amounts of impuri-
ties on the physical and chemical properties of pure aluminium.
The following analyses are of considerable historic interest as
showing incidentally the improvement which has been made in
the quality of the commercial metal since the beginning of the
industry :
54
ALUMINIUM.
Aluminium.
1. Deville Process 88.350
2. " " 92.500
3. " " 92.000
4. " " 92.969
5. " " 94-700
6. " " 96.160
7. Tissier Bros 94.800
8. Morin & Co., Nanterre 97.200
9. " " 97.000
10. " " 98.290
11. " " 97.680
12. Merle & Co., Salindres 96.253
13. " " 96.890
14. " " 97-400
15. " " 97.600
16. Frishmuth 97-49
17- " 97-75
18. Hall's Process 98-34
19. Deville-Castner - . 99.20
20. Grabau Process 99.62
21. " " 99-So
22. Hall's Process 99-93
Silicon.
Iron.
2.87
2.40
0.70
6.80
0.45
7-55
2.149
4.88
3-70
1.60
0.47
3-37
4.40
0.80
0.25
2.40
2.70
0.30
0.04
1.67
0.12
2.20
0.454
. 3-293
1.270
1.840
1. 00
1.30
0.40
1.40
1.90
0.61
1.70
0.55
1-34
0.32
0.50
0.30
0.23
0.15
0.12
0.08
0.07
trace.
Notes on the above analyses :-
2
and
3-
4-
5-
7-
8.
9-
[O,
II.
12, 13.
14. 15-
16.
Analyzed by Salvetat. Contained also 6.38 per cent, of copper and a trace
of lead.
Analyzed by Dumas.
Parisian aluminium bought in La Haag,
Analyzed by SalvStat. Contained also a trace of sodium.
Parisian aluminium bought in Bonn and analyzed by Dr. Kraut.
Made at the works near Rouen, in 1858, from cryolite. Analyzed by
Demond^ur.
Analyzed by Sauerwein. Contained also traces of lead and sodium.
Analyzed by Morin. Average of several months' work.
Analyzed by Kraut. Represents the best product of the French works
sent to the London Exhibition in 1862.
Analyzed by Mallet. The best metal v/hich could be bought in 1880.
Purchased in Berlin by Mallet, and used by him as the material which
he purified and used for determining the atomic weight of aluminium.
Analyzed by Hampe. This was the purest metal which could be bought
in 1876. No. 14 contained also o.io per cent, of copper and 0.20 per
cent, of lead. No. 15 contained 0.40 per cent, of copper and 0.20 per
cent, of lead.
Bought in Philadelphia as Frishmuth's aluminium, in 1885, and analyzed
by the author.
PHYSICAL PROPERTIES OF ALUMINIUM. 55
17. Specimen of the metal composing the tip of the Washington Monument,
cast by Frishmuth. This analysis is reported by R. L. Packard m the
Mineral Resources of the United States, 1883-4.
18. The best ordinary grade of metal made by this process, analyzed by Hunt
& Clapp, Pittsburgh. For average analyses, etc., see description of pro-
cess.
19. The best grade made by this process, exhibited at the Paris Exposition,
1889. Analyzed by CuUen.
20. Analysis by Dr. Kraut of metal being made on a commercial scale.
21. Analysis by Grabau of the purest metal yet obtained by his process.
22. Made from chemically pure alumina, in order to determine what degree of
purity was attainable by the electrolytic processes.
In addition to the above, the following analyses made in the
Pittsburgh Testing Laboratory show the quality of commercial
aluminium which has been put on the market in recent years :
Com- Graphi-
Alumin- bined toidal
Second Quality Metal. ium. Silicon. Silicon. Iron. Copper. Sodium. Lead.
Pittsburgh Reduction Co 9S-00 1.50 1.35 2.00 0.07 0.04 0.03
Society Anon, de TAluminium .. 95.00 0.90 i.oo 3.00 0.05 o.oi 0.04
Alliance Aluminium Co 95-00 0.90 0.75 3.25 0.02 0.07 o.oi
The Aluminium Co., Limited . . . 95.00 0.85 0.75 3.00 o.io 0.30 nil
The Al. LA. G., Switzerland ... 95.00 1.75 1.15 2.00 o.ci 0.07 nil
" " " ... 94.15 1.02 0.54 2.80 1.49 — —
First Quality Metal.
Pittsburgh Reduction Co 97.00 1.55 1.25 0.13 0.03 0.02 0.02
Soc. Anon, de I'Al 97.00 0.90 0.82 1.20 0.04 o.oi 0.03
Alliance Al. Co., Ltd 97.00 0.95 0.53 1.45 0.01 0.05 o.oi
The Al. Co., Limited 97.00 0.75 0.52 1.55 0.03 0.15 nil
Pittsburgh Reduction Co 98.00 1.30 0.60 0.07 o.oi o.oi o.oi
Soc. Anon, de I'Al 98.00 0.71 0.35 0.90 o.oi o.oi 0.02
Alliance Al. Co., Ltd 98.00 0.90 0.29 0.75 o.oi 0.04 o.oi
The Al. Co., Limited 98.00 0.90 0.23 0.80 0.02 0.05 nil
Pittsburgh Reduction Co 98.52 0.42 0.72 0.05 0.06 nil 0.04
" " " 99.00 0.80 0.15 0.03 O.OI nil O.OI
Soc. Anon, de I'Al 99-00 0.35 0.13 0.50 nil o.oi o.oi
Alhance Al. Co., Ltd 99.00 0.31 0.20 0.45 nil 0.03 o.oi
The Al. Co., Limited 99-°° °-^l °-'S o-5S °-°2 o.oi nil
Pittsburgh Reduction Co 99-20 041 0.34 0.05 nil nil nil
Alliance Al. Co., Ltd 99- H o-23 0.17 0.46 nil nil nil
Pittsburgh Reduction Co 99-34 °A° 0-21 0.05 nU nil nil
The makers represented above are :
The Pittsburgh Reduction Company. New Kensington, Pa.
56 ALUMINIUM.
The Alliance Aluminium Company, Limited. Wallsend-on-
Tyne, England.
The Aluminium Company, Limited. Oldbury, near Birming-
ham, England.
The Societe Anonyme de I'Aluminium. Nanterre, France.
The Aluminium Industrie Actien-Gesellschaft. Neuhausen,
Switzerland.
The second, third and fourth of these firms used the sodium
process, the others the electrolyic methods. It is at once seen
that for metal with the same proportion of aluminium, that
made by the electrolytic processes contains less iron, but more
silicon, than that made by the sodium processes ; there is no
observable regularity in the proportion of combined and graph-
itoidal silicon to the amount of iron. On an average, the graph-
itoidal silicon is about one-third to two-thirds of the combined
silicon.
Rammelsberg (Kerl's Handbuch) investigated the question
of the different states of silicon in aluminium. He found in
aluminium reduced from cryolite by sodium in a porcelain cru-
cible, that on treatment with hydrochloric acid, the combined
silicon changes into silica, or part escapes as silicon hydride,
while the graphitoidal silicon remains as a black residue. Two
analyses gave him the following results :
1.. 2.
Silicon obtained as silica 9.55 1.85
Free silicon 0.17 0.12
Silicon escaping in SiH'' 0.74 0.58
In aluminium containing 6.20 per cent, of total silicon, ana-
lyzed in the Pittsburgh Reduction Co.'s laboratory, 3.85 per
cent, was graphitoidal silicon. In another specimen, contain-
ing 5 -30 per cent, of total silicon, 2.40 per cent, was graphi-
toidal.
An experiment, made at the Pittsburgh Testing Laboratory,
to determine the influence of quick or slow cooling on the con-
dition of the silicon, showed that the chilled metal contained,
slightly more of the silicon in the graphitoidal state and less in
the combined state than metal slowly cooled.
PHYSICAL PROPERTIES OF ALUMINIUM. 57
This result is the opposite of the behavior of carbon in iron,
and it is found, as might be expected, that no appreciable dif-
ference in hardness can be detected between the surfaces of
ingots cast in chills and those cast in hot moulds.
M. Dumas found that aluminium usually contains gases,
about which he makes the following statements:* On submit-
ting aluminium in a vacuum to the action of a gradually increas-
ing temperature up to the softening point of porcelain, and
letting the mercury pump continue acting on the retort until it
was completely exhausted, considerable quantities of gas were
withdrawn. The liberation of the gas from the metal seems to
take place suddenly towards a red-white heat. 200 grammes
of aluminium, occupying 80 c.c, gave 89.5 c.c. of gas, meas-
ured at 17° and 755 mm. pressure. The gas consisted of 1.5
c.c. carbonic acid, and 88 c.c. hydrogen. Carbonic oxide,
nitrogen and oxygen, were absent.
The author has observed that molten aluminium will absorb
large quantities of gas. On passing sulphuretted hydrogen
into the melted metal for about twenty minutes some aluminium
sulphide was formed, while the metal appeared to absorb the
gas. On pouring, the metal ran very sluggishly, with a thick
edge, but when just on the point of setting, gas was disengaged
so actively that the crackling sound could be heard several feet
away, and the thick metal became suddenly quite fluid and
spread over the plate in a thin sheet. The gas disengaged
seemed by its odor to contain a large proportion of sulphur-
etted hydrogen, although free hydrogen may have been pres-
ent in it.
Le Verrier has established the presence of carbon in small
amount in commercial aluminium.! Taking a large quantity of
metal and treating it with a current of hydrochloric acid or
hydriodic acid gas, entirely free from oxygen, there remains a
grey residue. This, treated with dilute hydrochloric acid, gives
a very light residue of amorphous carbon, of a maroon color,
* Comptes Rendus, xc, 1027 (1880).
t Comptes Rendus, July, 1894, p. 14.
58 ALUMINIUM.
■which, on being separated out, can be entirely burnt to car-
bonic acid gas in a current of oxygen. This carbon does not
contain a trace of graphite ; it is entirely amorphous. It is
easiest estimated by dissolving ten grammes of aluminium in a
concentrated solution of caustic potash, washing the residue
with water, drying, burning in a current of oxygen, and weigh-
ing the carbonic acid formed. In three specimens tested there
were found 0.104, O.108 and O.080 per cent, of carbon respect-
ively. To determine the effect of carbon on the physical prop-
erties of aluminium, he melted best quality metal, cast a
specimen ingot, and then dissolved in it some crystallized
aluminium carbide, AhCs (for method of making this see Chap-
ter XIV) . A specimen of the carburized metal was then cast
and tested. The results were as follows; the weights being per
square millimetre of section :
Cast Specimens.
Elastic Limit. Breaking Load. Elongation.
Pure aluminium — 1 1. 1 kilos. 9 per cent.
Carburized aluminium — 6.5 " 5 "
— 8.6 " 3 "
Rolled Specimens.
Elastic Limit. Breaking Load. Elongation.
Pure aluminium, hard 23 kilos. 25.0 kilos. 2.0 per cent.
" " annealed 8 " 14.0 " 23.0 "
Carburized aluminium, hard 20 " 20.79 " 2.5 "
" " annealed 7.7 " 13.80 " 26.5 "
It would appear that the cast metal shows the greatest de-
terioration by the presence of carbon.
Le Verrier also proved the presence of traces of nitrogen in
commercial aluminium by passing the hydrogen evolved during
solution in dilute caustic potash into a Nessler solution, which
then gives the ammonia reaction. To determine the exact
effect of nitrogen, some aluminium was melted and a current of
nitrogen passed into it. The metal became saturated with the
gas, and showed the following diminution in strength :
PHYSICAL PROPERTIES OF ALUMINIUM. 59
Cast Specimens.
Elastic Limit, Breaking Load. Elongation.
Pure aluminium 7.5 kilos. i I.I kilos. 9 per cent.
Aluminium saturated with nitrogen 6.5 " g.6 " 6 "
Le Verrier considers that nitrogen and carbon occur in alu-
minium in the state of aluminium nitride and carbide re-
spectively, dissolved in the excess of aluminium. The same
investigator has discovfered by the microscope, in the residue
left by dissolving in hydrochloric acid, very small, sharp crys-
tals of boron carbide, the boron coming from the boric acid
used in agglomerating the carbon electrodes. A little amor-
phous alumina is also sometimes to be found.
Color.
Deville : The color of aluminium is a beautiful white with a
slight blue tint, especially when it has been strongly worked.
Being put alongside silver, their color is sensibly the same.
However, common silver, and especially that alloyed with
copper, has a yellow tinge, making the aluminium look whiter
by comparison. Tin is still yellower than silver, so that alu-
minium possesses a color unlike any other useful metal.
Mallet: Absolutely pure aluminium is perceptibly whiter
than the commercial metal ; on a cut surface very nearly pure
tin- white, without bluish tinge, as far as could be judged from
the small pieces examined.
The purest-looking aluminium examined by the author is
that made by Grabau. On a fresh fracture it is absolutely
■white, but on long exposure to the air it takes a faint, almost
imperceptible bluish tint. On a cut surface it has the faintest
suspicion of a yellow tint, not so decided as the yellowish color
of pure tin. Ordinary commercial aluminium is bluish on a
fresh fracture, the tint being deeper the greater the amount of
impurities it contains. A specimen with 10 per cent, of silicon
and 5 per cent, of iron was almost as blue as lead. It is my
belief that a very small percentage of copper closes the grain
-and whitens the fracture a little; I have also found that chilling
6o ALUMINIUM.
suddenly from a high temperature has the same effect. Wheir
ingots of aluminium are exposed a long time to damp air, the
thin film of oxide forming on them gives a more decided bluish
cast to the metal, since the coating is perfectly snow-white and
hence, by contrast, heightens the bluish tint of the metallic
background. Mourey recommended removing this discolora-
tion by placing the articles first in dilute hydrofluoric acid,
1,000 parts of water to 2 of acid, and afterwards dipping in
nitric acid. The oxide would thus be dissolved and the original
color restored. Pure aluminium possesses to the highest de-
gree that property expressed best by the French term " eclat."
It is rather difficult to see why the blue tint should be more
prominent after the metal has been worked, yet I think two
reasons will explain this phenomenon ; first, aluminium is not a
hard metal, and on polishing or burnishing, particles of dirt or
foreign substances are driven into the pores of the metal,,
thereby altering its color slightly ; second, any metal looks
whiter when its surface is slightly rough than when highly
polished, in the latter case it being as much the reflected color
of the general surroundings as the color of the metal itself
which is seen. I have never seen any highly polished white
metal which did not look bluish, especially when reflecting out-
door light. I think this explains why opera-glasses, rings,
jewelry, etc., generally look bluer than the bar or ingot-metal
from which they are made.
Aluminium takes a very beautiful mat, which keeps almost
indefinitely in the air, the surface thus slightly roughened ap-
pearing much whiter than the original polished surface. Alu-
minium can be polished and burnished without much difficulty
if attention is given to a few particulars which it is necessary to
observe. (For methods of poHshing, etc., see Chapter XIII.)
Extremely thin films of aluminium are fine violet-blue by
transmitted light.
Fracture.
A cast ingot of purest aluminium has a slightly fibrous
structure, a section y^ inch thick bending twenty degrees or
PHYSICAL PROPERTIES OF ALUMINIUM. 6 1
SO from a straight line when sharply bent before showing cracks
at the outside of the turn. The fracture of such an ingot is
uneven, rough, and very close, often showing a curious semi-
fused appearance, as if it had been already exposed to heat and
the sharpest points melted down. However, only the purest
varieties show these peculiarities. Metal containing 96 to 97
per cent, of aluminium begins to show a crystalline structure,
breaks short, and with a tolerably level surface. Metal less
than 95 per cent, pure shows large shining crystal surfaces on
the fracture, the smaller crystals being on the outside of the
ingot where it has been cooled most quickly, while in the cen-
tre the crystalline surfaces may be as large as tV inch in
diameter. A specimen containing only 85 per cent, of alumin-
ium broke as short as a bar of antimonial lead, with a large
granular, crystalline surface.
Working the metal increases its fibrousness greatly, the sec-
tion of a square rolled bar of good metal looking very much
like that of a low-carbon steel.
Hardness.
The purest aluminium is distinctly softer than the commer-
cial ; estimated on the scale of hardness proposed by Mohs it
would be written as about 2.5, that is, a little harder than can
be scratched by the nail. It is not so soft as pure tin. The
presence of impurities, however, rapidly increases the hardness.
While 99 per cent, aluminium can be cut smoothly with the
knife and shavings turned up almost as with pure tin, yet 95
per cent, metal can hardly be cut at all ; the shavings break off
short, and a fine grating is felt through the blade.
Aluminium becomes surface hardened by cold working.
Castings of aluminium drop-forged cold, in dies, are made
sensibly harder and thus adapted for standing more wear.
Cold drawing or rolling gives to it nearly the hardness of brass.
In a drop test to investigate this quality made in the Pittsburgh
Testing Laboratory, the following comparative results were
reached :
62 ALUMINIUM.
Hardness.
Aluminium, rolled 62
Aluminium, cast 47
Brass, rolled 86
Brass, cast 71
Copper 100
Experience in testing various specimens of commercial alu-
minium with the knife will, I am sure, enable a person to be-
come quite skillful in determining the purity and in separating
different grades from each other. Taking this test in connec-
tion with the breaking and surface of fracture, it appears to me
that these indications are as significant and can be made of as
much use as the corresponding tests for iron, steel, and other
metals. Mr. Joseph Richards, the author's father, having had
many years' experience in testing lead, tin, zinc, and similar
metals, in which the knife-blade has been put to good service,
has been able with very little practice to arrange a number of
specimens of aluminium correctly according to their purity sim-
ply by noting carefully the way they cut and the color of the
cut surface. These tests will in the future, I am sure, be of
great use to those handling aluminium on a large scale, es--
pecially in the works where it is produced.
Specific Gravity.
Mallet: The specific gravity of absolutely pure aluminium-
was carefully determined at 4° C, and the mean of three
closely agreeing observations gave 2.583.
Commercial aluminium is almost always heavier than this,
but the increase is not in direct proportion to the amount of
impurities present. There are two reasons why this last state-
ment is correct; first, we cannot say what expansion or con-
traction may take place in forming the alloy; second, while-
most of the impurities which occur are much heavier than alu-
minium, yet silicon, the most frequent of all, has a specific
gravity of only 2.34 (Deville's determination), and therefore
acts in the opposite direction to the other impurities, though.
PHYSICAL PROPERTIES OF ALUMINIUM. 63
not to SO great an extent. The following analyses and specific
gravities may give some information on this point: —
Analysis.
Specific Gravity.
Aluminium.
Silicon.
Iron.
Observed.
Calculated.
97.60
0.60
1.80
2-73S
2.61 (2.64)
95-93
2.01
2.06
2.800
2.61 (2.69)
94.16
4-36
1.48
2.754
2.59 (2.74)
78.-
16.—
4-—
2.85
2.66
It is seen in each case that the calculated specific gravity is.
much less than the observed, which would show contraction in
volume by alloying. Indeed, this is a prominent characteristic
of aluminium alloys, aluminium often taking up several per
cent, of its weight of another metal without its volume being
increased, the particles of the other metal seeming to pass be-
tween those of the aluminium ; thus probably accounting for
the extraordinary strength and closeness of many of the alumin-
ium alloys. This subject is treated more at length in the chap-
ter on alloys. We can see the large contraction taking place
by inspecting the numbers in parentheses under the heading
"Calculated." These are computed on the supposition that
the volume of the impure aluminium is equal to that of the
pure aluminium entering into it. As these numbers are also-
less than the observed specific gravities, the extraordinary fact
is shown that aluminium can absorb several per cent, of iron
and silicon and yet will decrease in volume in doing so.
The remarks thus far made are based on the gravity of cast
metal. Aluminium increases in density by being worked : De-
ville states that metal with a specific gravity of 2.56 had this
increased to 2.67 by rolling, which, he says, may explain the
diflerences existing in its properties after being annealed or
worked. He remarked further that heating this rolled metal to
100°, and cooling quickly, changed its specific gravity very little,
lowering it to 2.65. I have observed that on heating a piece of
aluminium almost to its fusing point and suddenly chiUing it in
water, its specific gravity was lowered from 2.73 to 2.69.
64 ALUMINIUM.
Experiments made by Prof. J. W. Langley with aluminium
98.52 per cent, pure, the rest being mostly silicon, gave its
specific gravity as follows :
Sample sawn from centre of a cast ingot 2.587
Same, annealed 2.692
Rolled into sheet 0.0625 inch thick 2.710
Stamped into medals 2.725
The low specific gravity of aluminium, when compared with
that of the other metals, is (in the words of a recent lecturer)
" the physical property on which our hopes of the future use-
fulness of aluminium chiefly rest." The following table will
facilitate this comparison :
Specific Gravity.
Alumin- Founds in a Kilos in .1
Water = I. ium =: i. cubic foot. cubic meter.
Platinum 21.5 8.3 1344 21,500
Gold 19.3 7.4 1206 19,300
Lead 11.4 4.6 712 11,400
Silver 10.5 4.0 656 10,500
Copper 8.9 3.5 557 8,900
Iron and steel 7.8 2.8 487 7,800
Tin 7.3 2.7 456 7,300
Zinc 7.1 2.7 444 7,100
Aluminium 2.6 i.o 163 2,600
In comparing the price of aluminium with that of a metal
which it might replace, for purposes where the bulk of the arti-
cle is fixed, it is of first importance to take this low specific
gravity into account. When we come to consider closely, we
find that almost every article of use or ornament is wanted of a
fixed size, and therefore the real basis of comparison of prices is
that of a fixed volume of the metal rather than a fixed weight.
To facilitate this comparison, I give below the actual market
prices of one pound weight of the common metals, with the
prices of equal volumes:
PHYSICAL PROPERTIES OF ALUMINIUM. 65
Value of Relative cost Value of Relative cost
I pound, of equal weights, i cubic foot, of equal volumes.
Silver jSio.oo 2850 ;J656o.oo 1 1430
Nickel 0.50 140 279.00 468
Aluminium 0.35 100 S7-S0 10°
German silver 0.30 85 167,00 290
Tin 0.15 43 68.50 120
Bronze 0.15 43 79.00 137
Brass 0.12 34 61.75 107
Copper o.io 28 55.75 97
Lead 0.04 11 28.50 50
Zinc 0.04 II 17-75 3'
Steel 0.02 6 9.75 17
Cast Iron o.oi 3 5.00 8
It is therefore evident, that for almost all uses to which
aluminium is applicable, there are only five of the common
metals which are cheaper, viz., copper, lead, zinc, steel and cast-
iron. When it is further remembered that the cost of the metal
alone usually forms only a small part of the value of the finished
article, it can be further asserted that there should be only a
trifling diflference between the cost of an article made in alu-
minium and one of tin, bronze, brass or copper. The sole
reason why aluminium articles are not sold more cheaply at
present, lies in the fact that they are not made and sold in such
large quantities ; the increase of the aluminium industry will
therefore ensure lower prices for aluminium goods.
Fusibility.
Deville : Aluminium melts at a temperature higher than that
of zinc, lower than that of silver, but approaching nearer to that
of zinc than silver. It is, therefore, quite a fusible metal.
Mallet : It seems that pure aluminium is a Httle less fusible
than the commercial metal.
Pictet determined the melting point to be 600°, Heeren about
700°, while Van der Weyde placed it as high as 850°. On a
sample containing 0.5 per cent, of iron, Carnelly determined
the melting point at 700° ; with 5 per cent, of iron it did not
fuse completely until 730°. The discordance between these
various experimenters lies chiefly in the errors of the pyro-
S
66 ALUMINIUM.
meters used. Since the perfection of the electric pyrometer by
Le ChateHer, the melting point of the purest aluminium has
been repeatedly observed as very close to 625°. This figure
is probably correct within 5°.
A very small admixture of iron and silicon lowers the melt-
ing point. Le Chatelier found with a metal containing 1.50
per cent, silicon and 0.75 per cent, iron, the melting point
619°- A larger quantity of either of these elements quickly
operates in the other direction, and prevents fluid fusion until
a temperature above 625° is reached.
Spring has determined that aluminium powder flows to a
solid mass at a pressure of 38 tons per square inch, at ordinary
temperatures.
Volatilization.
Deville : Aluminium is absolutely fixed, and loses no part of
its weight when it is violently heated in a forge fire in a carbon
crucible.
This statement was made in 1859, and can still be accepted
as true as far as ordinary furnace temperatures are concerned.
But, with the use of the electric furnace, temperatures have
been attained at which aluminium does sensibly volatilize. In
Cowles Bros, electric furnace it is stated that the aluminium is
almost all produced as vapor and as such is absorbed by the
copper or iron present ; when these are not present it is found
condensed in the cooler upper part of the furnace. A similar
experience has been met in other electric furnace processes, so
that the volatilization of aluminium at these extreme tempera-
tures may be accepted as a fact.
Aluminium vapor has been recently produced in an electric
furnace in large enough amounts to determine that it is of a
green-blue color.
Odor.
The purest aluminium has no perceptible odor, but metal
containing i per cent, or more of silicon exhales the odor of
silicon hydride, exactly the same odor as proceeds from cast
PHYSICAL PROPERTIES OF ALUMINIUM. 6^
iron. Second quality commercial aluminium gives this smell
quite strongly, but in the present first quality metal it is difficult
to detect it except by smelling immediately after a brisk
rubbing.
Taste.
The same remark may be made regarding taste as of the
odor. The purest metal has no taste ; the impure tastes like
iron, but not so strongly.
Magnetism.
Deville, as also Poggendorff and Reiss, state that aluminium"
is very feebly magnetic. It must be remembered, however, that
they tested metal made by the sodium process, which almost
invariably contained iron.
Prof. Frank Very, of the Allegheny Observatory, Allegheny,
Pa., finds aluminium with only a trace of iron to be absolutely
non-magnetic. With 0.05 per cent, of iron, none could be ob-
served. An ingot containing 1.5 per cent, iron showed faint
polarity, while with 2 per cent, the polarity was very decidedly
observed.
Since the present first quality commercial aluminium contains
less than 0.2 per cent, of iron, and frequently only 0.05 per
cent., we may observe that this is less than is usually found in
commercial brass, bronze or german-silver, and for this reason,
as well as its other valuable properties, aluminium answers very
well for compass boxes or cases, or parts of electrical instru-
ments where non-magnetic properties are desired.
Sonorousness.
Deville: "A very curious property, which aluminium shows
the more the purer it is, is its excessive sonorousness, so that
a bar of it suspended by a fine wire and struck sounds like a
crystal bell. M. Lissajous, who with me observed this prop-
erty, has taken advantage of it to construct tuning forks of
aluminium, which vibrate very well. I also tried to cast a bell,
which has been sent to the Royal Institution at London at the
-68 ALUMINIUM.
request of my friend Rev. J. Barlow, vice-president and secre-
tary of the institution. This bell, cast on a model not well
adapted to the qualities of the metal, gives a sharp sound of
considerable intensity, but which is not prolonged, as if the
clapper or support hindered the sound, which, thus hindered,
becomes far from agreeable. The sound produced by the in-
gots is, on the contrary, very pure and prolonged. In the ex-
periments made in Mr. Faraday's laboratory, this celebrated
physicist has remarked that the sound produced by an ingot of
aluminium is not simple. One can distinguish, by turning the
vibrating ingot, two sounds very near together and succeeding
each other rapidly, according as one or the other face of the
ingot faces the observer."
The bell referred to above was 20 kilos in weight and 50
centimetres in diameter, but as Deville admits, its sound was
not pleasing, and a contemporary writer, evidently not very
enthusiastic in sounding the praises of aluminium, said that
" while the bell was highly sonorous, yet it gave a sound like
a cracked pot."
I have not heard that any large bell has since been cast, but
it is certain that the metal in bars has a highly musical ring.
Faraday's observation has also been verified, for a recent lec-
turer suspended by one end a bar 6 feet long 31^ inches wide,
and I y^ inches thick, and on striking it a prolonged vibration
ensued, two notes being recognized, A sharp and D sharp, the
latter more subdued.
Within the last few years aluminium has been extensively
employed for sounding boards in public hails, the sounding
boards of pianos, and even for the construction of horns and
violins. The sounding board in the Lyceum Hall, New York
city, is an example. The particular advantage is, its not being
affected by a moist atmosphere. Dr. Alfred Springer, of Cin-
cinnati, in speaking of its use for sounding boards says,* " It
.differs from all other metals in the absence of the comparatively
* Trans. A. A. Adv. Science, 1891, vol. 40, p. 182.
PHYSICAL PROPERTIES OF ALUMINIUM. 69
continuous and uniform higher partial tones, which give in
other metals the tone-color called " metallic," and further, that
it also possesses an elasticity capable of sympathetic vibration
uniformly through a wide range of tone-pitch, which renders it
in this respect superior to wood."
Dufour has measured the velocity of sound in aluminium at
4950 metres per second, almost the same figure as for steel.
Crystalline Form.
Deville : " Aluminium often presents a crystalline appearance
when it has been cooled slowly. When it is not pure, the little
crystals which form are needles, and cross each other in all
directions. When it is almost pure it still crystallizes by fusion,
but with difficulty, and one may observe on the surface of the
ingots hexagons which appear regularly" parallel along lines
which centre in the middle of the polygon. It is an error to
conclude from this observation that the metal crystallizes in the
rhombohedral system. It is evident that a crystal of the regu-
lar system may present a hexagonal section; while on the
other hand, in preparing aluminium by the battery at a low
temperature, I have observed complete octahedrons which were
impossible of measurement, it is true, but their angles appeared
equal."
By slowly cooling a large body of melted aluminium and
pouring out the fluid interior, distinct octahedrons may be
observed.
Elasticity.
Cast aluminium is not very elastic; it may be likened in this
respect to cast silver. When worked, however, it becomes
more rigid and elastic.
Mallet remarked that absolutely pure aluminium seemed to
be less hardened by hammering than ordinary commercial
metal.
Cast aluminium stiffens up very quickly in rolling or drawing,
and the strains set up in the metal can be removed by an
yo ALUMINIUM.
annealing, which consists in heating the metal to an incipient
red heat and then either allowing to cool slowly, or leaving a
few minutes at that heat and then cooling quickly by plunging
into water. Metal thus treated becomes very soft and pliable,
hardly any more elastic than lead, and will stand considerable
working before it again becomes stiff and elastic. The presence
of 2 to 5 per cent, of copper, nickel, silver, German-silver or
titanium increases very greatly the elasticity of aluminium
without increasing noticeably its specific gravity or impairing
its malleability.
Tensile and Compressive Strength.
W. H. Barlow* was the first to carefully test the tensile
strength of aluminium. He used a rolled bar one-quarter
inch square. With -a test piece two inches long, the tensile
strength was found to be 26,800 pounds per square inch, with
elongation before breaking of 2.5 per cent.
Kamarschf tested aluminium wire, and obtained an average
of 12.5 kilos per square millimetre, equal to nearly 18,000
pounds per square inch. This wire must have been annealed,
while the bar tested by Barlow was worked stiff before testing.
Mr. Spilsbury, of the Trenton Iron Co., obtained with alu-
minium wire of one-sixteenth inch diameter a tensile strength
of 62,300 pounds per square inch, the wire having been drawn
with one annealing from a wire-rod one-sixth inch in diameter.
The same wire made 47 bends at a right angle before breaking.
A most valuable series of mechanical tests of aluminium
have been made by the Pittsburgh Reduction Company, and
are copied as follows| :
* Rpt. British Assoc. Adv. Science, 1882, p. 668.
fDingler, Vol. 172, p. 55.
J Transactions Am. Inst. Mining Engineers. Vol. XVIII., p. 528 (1890).
PHYSICAL PROPERTIES OF ALUMINIUM.
Tensile Tests.
n
No. I quality commercial metal, averaging
over 98 per cent. pure.
Ordinary castings of over \ inch sectional
area, as cast ....
Same, annealed
Same castings, hardened by drop forging cold
Rolled bars, left hard
Same, annealed
Hammered bars, left hard
Same, annealed
"Wire i to J inch diameter, as drawn
Same, annealed
Wire y\ to -^^ inch diameter, as drawn
Wire ^ to ^ J ^ inch diameter, as drawn
Same, annealed
Plates to \ inch thick, as rolled
Same, annealed
Sheets \ to -^-^ inch thick, as rolled
Same, annealed
Sheets ^V '° ttss '^^'^ 'C!\\<^, as rolled
Same, annealed
•a 3 §
6,132
6,600
10,000
16,000
13.870
14,630
14,000
12,000
10,870
32,000
26,000
21,000
9.300
8,500
12,500
10,700
13.500
11,000
c
»H 4) u
■a p-.s
rt ^ rt
15,640
17,100
24,000
32,500
25,000
24,120
22,000
24,500
22,830
54,000
49,000
33,000
22,740
17.740
25,000
21,070
27,500
23,000
•a .
& O
a a
4) j-j •
"S "> So
8.66
15.00
18.00
42.00
49.11
3S-H
43.00
58.46
65-57
68.00
54.00
62.00
12.40
13-73
35-50
39.00
40.00
43-50
3,000
3,500
3.000
6,000
6,000
5.500
5,500
4,500
4,500
12,000
10,000
7,000
4,000
4,000
4.500
4,500
4,500
4,500
72
ALUMINIUM.
Compressive Tests.
Same metal is in above tensile
tests, about 98 per cent. pure.
Ordinary casting, as cast
Same, annealed
Same, hardened by drop forging.
Rolled bars, left hard
Same, annealed
Hammered bars, left hard
Same, annealed
Metal containing 4.5 per cent,
silicon and 1.5 per cent, iron,
casting, unannealed
Metal containing 1.14 per cent,
silicon and 0.05 per cent, iron,
castings, unannealed
Same, larger test-piece
.d
DA .
•S.J-
g^^
•= 0. c
"»-S a
e »■"
a-"
0, a <u
imat
n po
quar
^^ .« (fl
S
P
3.565
12,730
2,037
10,185
4,583
15,275
2,263
9,054
2,043
6,809
5,659
11,32c
5,094
11,320
4,800
15-275
4,583
12,730
5,094
11,320
'u a
Height X diam.
I in. X 0.5 in.
I in. X 0.5 in.
I in. X 0.5 in.
1.5 in. X 0.75 in.
1.5 in. X 0.75 in.
m. XI.5 m.
in. X 1.5 in.
I m. X0.5 m.
I in.xo.5 in.
3 in. X 1.5 in.
Height X diam.
0.985 X 0.503
0.975 * 0.506
0.965 X 0.508
1.459x0.760
1.468x0.756
2.91 X 1.520
2.91 X 1.519
0.965 X 0.508
0.975 X 0-507
2.92 X 1.519
Transverse Tests.
Metal containing 98.52 per cent, aluminium,
1. 14 per cent, silicon, and 0.05 per cent. iron.
Test-piece one inch square, supported on knife
edges 24 inches apart, loaded in the centre . . .
Same metal, test-piece a 1.5 inch diameter rolled
bar, on knife-edges 12 inches apart, loaded in
the centre
Load,
Deflection,
Permanent
pounds.
inches.
set, inches.
50
/l
A
100
S^
—
150
w
W
175
11
—
200
II
\%
225
H
—
250
III
m
275
If?
m
300
2H
2A
Not
ruptured.
1,000
A
0
1,500
A
A
2,000
M
A
2,500
H
—
2,800
\\
—
Broke.
PHYSICAL PROPERTIES OF ALUMINIUM.
7Z
From the various tests above enumerated, Messrs. Hunt,.
Langley and Hall draw the following general conclusions :
The average strength of commercial aluminium of the follow
ing average composition :
Aluminium 97. to 99. per cent.
Graphitic silicon o.i to i.o "
Combined " 0.9 to 2.8 "
Iron 0.04 to 0.2 "
is as follows :
Elastic limit in tension.
i- Castings.
Sheet . . .
Wire....
I Bars
Pounds per square inch.
6,500
12,000
16,000-30,000 (according to fineness)'
14,000
Ultimate strength in ten-
sion
15.000
24,000
30,000-65,000 (according to fineness)
28,000
Percentage of reduction
Castings .
Sheet...
r
iction j
of area, in tension .... ] Wire
L Bars.
15 per cent..
35 "
60 "
40 "
Pounds.
Elastic limit in compression in cylinders with length twice the diameter 3,50o
Ultimate strength ■ 12,000
Modulus of elasticity, castings 1 1,000,000
" " cold-drawn wire 19,000,000
" " sheets and bars 13,000,000
Professor Le Chatelier * has shown that the tensile strength
of annealed aluminium wire varies with the temperature as
follows :
Kilos per sq. millimetre. Pounds per sq. inch.
At 0° C. 1 8 26,000
150° 13 18,500
250° 7 1 0,000
300° 5 7^000
40o<^ 2 3,000
* Lejeal's Aluminium.
74 ALUMINIUM.
Minet found the following properties for aluminium strongly
worked and annealed :
Tensile strength. Elongation.
Kilos per sq. mm. Pounds per sq. in. Per cent.
After working 23.5 33iOOO 3
After being annealed I hour at 400° 15.1 21,500 17
He concludes from these results that, by careful annealing at
proportionate temperatures and for proportionate times, any
given strength between these limits may be obtained, or any
■desired elasticity from 3 to 17 per cent.
The results obtained for the tensile strength of aluminium
show, in general, that it is greatly influenced by the amount of
work done on the metal ; that while the pure, unworked metal
is by no means rigid, but elongates 10 to 20 per cent, before
breaking, as it is worked it becomes stififer and more elastic, its
strength may be nearly doubled, but it becomes at the same
time more brittle, as is shown by its elongation falling to 3 or 5
per cent. After working, increased elongation can be given to
it by annealing, but at the expense of ultimate strength. The
annealed material, however, would be a safer rhaterial to use in
any place where sudden shocks had to be sustained, if worked
within its elastic limit.
Taking the tensile strength of aluminium in relation to its
weight, it shows a very high mechanical value ; in fact, the only
material which can compare with it in tensile strength, weight
for weight, is the finest steel or aluminium bronze. A com-
parison on this basis is frequently made, in order to determine
the material which gives the greatest strength for a given
weight, or, rather, a given strength with the least weight. For
instance, we might make the comparison by calculating the
weight of rods of the different metals which would support a
certain maximum strain before breaking, and from these num-
bers derive a table of the relative weights of the metals to give
a certain strength :
PHYSICAL PROPERTIES OF ALUMINIUM. 75
Tensile strength, Relative strength Relative strength
Rolled Bars or Large Wire. pounds per sq. in. for same section, for same weight.
Aluminium 30,000 100 100
Cast steel 100,000 333 135
Soft steel 75,000 250 87
Wrought iron S5,oco 183 63
Aluminium bronze ....... 100,000 333 118
" brass 60,000 200 70
Gun bronze 35,000 117 37
Red brass 45,000 150 47
Copper 33,000 1 10 33
It results from this comparison that only steel of the highest
quality and the best aluminium bronze will give a greater
strength for a given weight than aluminium. Steel, however,
is subject to rust, whereas aluminium is not ; aluminium bronze
itself is a metal requiring considerable skill in working it to
always obtain the highest results ; these two are the only com-
petitors which aluminium has for constructions where great
strength combined with lightness is the first requirement, and
expense is a secondary consideration.
Malleability.
Aluminium stands high in the list of malleable metals. It
can be forged or rolled as easily as gold or silver, and can be
beaten out into leaf.
Mallet found that absolutely pure aluminium is decidedly
more malleable than the commercial metal, and is less hardened
by working. Experience in rolling it on a large scale has since
shown that the more impurity in the metal the harder it is to
work, and the quicker it will become hard and need annealing.
Some impurities, however, are more detrimental than others.
One per cent, of iron renders the metal stronger and harder to
roll, but more than this amount renders it less and less malle-
able, until with 6 per. cent, it is crystalline and brittle. On the
other hand, silicon may occur alone up to nearly 10 per cent,
without rendering the metal unfit for rolling.
Aluminium is most malleable between 100° and 150° C, and
can be worked some time at that temperature before becoming
76 ALUMINIUM.
hard. If rolled or worked cold, it needs more frequent anneal-
ing. While annealed aluminium is one of the softest and most
pliable metals, yet by cold working it can be given the stiffness
and temper of hard brass. The best commercial metal is
regularly rolled into sheets one-thousandth of an inch in thick-
ness, which sheets are sold for beating purposes, and it has
been rolled to one-half that thickness.
Metal for beating into leaf must be of the finest quality, i. e.,
over 99 per cent. pure. Rousseau, of Paris, was the first to
make aluminium leaf, and it was afterwards made for several
years by C. Falk & Co., of Vienna. At present, Mr. Kemp, of
New York, manufactures it on a large scale. The beating is a
little harder than is required for gold and silver, but by starting
with the purest aluminium equally thin leaf can be obtained.
A specimen of commercial aluminium leaf examined by the
writer had a thickness of 0.000638 millimetre, or one forty-
thousandth of an inch, which compares favorably with ordinary-
silver leaf. This leaf was opaque, but the thinnest attainable
leaf is a fine blue by transmitted light. No other useful metals
except gold and silver will show such malleability. This leaf is
now in regular use with gilders and decorators, and has en-
tirely superseded silver leaf because of its cheapness and non-
tarnishing qualities. The leaf is also rubbed into powder, and
in that state used as a metallic dust in printing and decorating.
Ductility.
Aluminium can be drawn into very fine wire. Even as early
as 1855, M. Vangeois made very fine wires with metal far from
being pure, and used them for making aluminium passementerie.
The metal quickly hardens at the drawing plate, and must be
frequently annealed. The larger sizes of wire can be drawn
warm, and then require less frequent annealing. The heated
gases from the chimney of an Argand burner will anneal the
very fine wires if they are simply passed across it. Wire as
fine as o.i millimetre (one two-hundred-and-fiftieth of an inch)
can be made without much trouble, while wire one-seventieth
PHYSICAL PROPERTIES OF ALUMINIUM. "JJ
of an inch in diameter is regularly kept in stock by the alu-
minium dealers.
Gold, silver, platinum, iron and copper are probably the only
metals more ductile than aluminium.
Expansion by Heat.
Fizeau determined that aluminium expands 0.00222 of its
length in passing from the freezing point to the boiling point,
or 0.0000222 of its length for a rise of 1° Centigrade, equal to
O.OOOOI129 per 1° Fahrenheit.
Prof. J. W. Langley examined metal 98.5 per cent, pure, the
rest being mostly silicon, and obtained for the expansion for
1° C. 0.0000206, which would be o.ooooi 15 for 1° F.
A bar of aluminium i foot long at 0° C. would, according to
Fizeau, be 1.00222 feet long at 100°, while a cubic foot of
aluminium at 0° would occupy 1.00666 cubic feet at 100° C,
since the rate of cubical increase is three times that of linear
expansion. This rate of expansion is close to that of tin,
among the common metals.
Specific Heat.*
The best experimenters have given various values for the
specific heat of aluminium, but it is very evident to the writer
that the differences are mainly due to differences in the purity
of the metal used. Professor Mallet used absolutely pure alu-
minium (purified for atomic weight determination), and the
writer used metal which analyzed 99.93 per cent, pure, and con-
tained but a trace of iron, while the other experimenters used
■ordinary commercial metal made by the sodium process and
■containing considerable quantities of iron.
Regnault, in 1855, used metal containing only 88.35 percent,
of aluminium. His figure of 0.2056, between 25° and 97°, is,
therefore, only approximate.
* For further details, see papers on this subject by the author in Journal of the
franklin Institute, April, 1892, and July, 1893.
78 ALUMINIUM.
In 1856, Regnault obtained metal 97 per cent, pure, with
which he obtained O.2122 (14° to 97°).
Kopp, in 1863, used Parisian aluminium containing two per
cent, of iron, and obtained a value varying between O.1970 and
0.2070 (20° to 52°). His results are unreliable.
In 1882, Mallet found the mean specific heat from 0° to 100°,
using absolutely pure aluminium, 0.2253.
Tomlinson * used commercial aluminium in wire, and gives
the following formula for the mean specific heat, from any
given temperature to 0° C. :
Sm = 0.2070 4" O.OOOI 151.
This would give from 0° to 100°, 0.2185.
Naccari f used commercial metal, and gives the following for-
mula, which expresses his results up to 300° C. :
Sm = 0.2116 + 0.0000475 *•
This would give from 0° to 100°, 0.2 164.
Le VerrierJ stated that he found, using best commercial
metal, the specific heat between 0° and 300° to be invariable,
and = 0.22 ; between 300° and 530° also constant, and = 0.30;
between 530° and 560° an absorption of heat, rendered latent,
of about 10 calories; between 540° and 600° the specific heat
again constant, and = 0.46. For the total quantities of heat
in the metal, at various temperatures, he gives :
o'' to 300° Q = 0.22 t.
300° to 530° Q = 65 + 0.30 (t— 300).
540° to 600° Q = 139 -\- 0.46 (t — 530).
About 600° Q = 170.
Before fusion at 620° Q = 200.
These determinations would give the mean specific heat
from 0° to 100°, 0.2200. No other investigator, however, has
noticed the sudden jumps noted by Le Verrier, which, if true,
*Proc. Royal Society, 1885, p. 494.
t Trans. Accademia di Torino, Dec, 1887.
I Comptes Rendus, 1892, Vol. 114, p. 907.
PHYSICAL PROPERTIES OF ALUMINIUM. 79
are indeed very singular. Experiments by Pionchon and the
writer, about to be described, gave no indications of such criti-
cal points.
Pionchon* states that he used very pure aluminium, and ob-
tained the following formulae :
291-86 t
0° to 580° Q = 0.393 t- giy.8 4- 1
625° to 800° Q = 0.308 t— 46.9.
(Molten.)
This would give the specific heat at 0°, = 0.2010; the
mean specific heat 0° to 100° = 0.2 130; heat in solid alu-
minium at its melting-point, 160.5 calories; heat in molten
aluminium at the setting-point, 239.4 calories ; specific heat of
molten aluminium constant, and = 0.308. The latent heat of
fusion would be 239.4 — 160.5 = 7^-9 calories.
The writer, using aluminium which analyzed 99.93 per cent,
pure, with only a trace of iron and 0.07 per cent, silicon, ob-
tained the following formulae for solid aluminium up to 600° :
Mean specific heat to o°- Sm = 0.2220 -|- 0.00005 t.
True specific heat at t°- S = 0.2220 -\- o.ocoi t.
Total heat to o°- Q = 0.2220 1 -|- 0.00005 t'.
These formulae give for the specific heat at 0° =0.2220;
the mean specific heat 0° to 100° = 0.2270; the heat in solid
aluminium at the melting-point, 158.3 calories; specific heat at
the melting-point, 0.285.
Regarding these figures, it will be observed that the mean
value 0° to 100° is less than i per cent, different from Mallet's
result, and therefore these values may be accepted as the true
value of the mean specific heat between those temperatures.
Regarding the value for the heat contained at the melting-point,
it is only a fraction over i per cent, removed from that given
by Pionchon's formula. It must not be forgotten, however,
that aluminium begins to soften at about 600°, and some of its
latent heat of fusion is absorbed before the true melting-point,
*Comptes Rendus, 1892, Vol. 115, p. 163.
So ALUMINIUM.
625°, is reached, as observed by both Pionchon and Le Verrier.
The numbers given by the formulae are the theoretical amounts
of heat which the metal would contain at 625°, provided that
none of the latent heat of fusion had been previously absorbed.
To determine the amount of heat in the molten metal at its
setting point the writer made several determinations by pour-
ing the metal into water, just as it was setting. The result
showed that the purity of the metal had a great effect on the
amount of heat thus given up.
Aluminium 96.9 per cent, pure gave up 229.0 calories.
99-9 " " " 254-0 "
99-93 " " " 258.3 "
It is seen that a small amount of impurity makes a large
difference, which is really caused by the impurity lowering the
melting point of the metal. Since the metal used by Pionchon
was not over 99.7 per cent, pure, we have a partial explanation
of why he obtained only 239.4 calories in the molten metal.
The figure deduced by the writer for the latent heat of fusion
of aluminium is therefore 258.3 — 158.3=100 calories.
The value of the specific heat of aluminium determined by
Mallet and the writer agrees best with Dulong and Petit's law,
as is seen by the following comparison of the actual and atomic
specific heats for the interval 0° to 100° :
Experimenter. Specific Heat x Atomic Weight= Atomic Heat.
Regnault 0.2122 x 27.0 = 5.73
Kopp 0.2020
Tomlinson 0.2185
Naccari 0.2164
Le Verrier 0.2200
Pionchon 0.21 30
Mallet 0.2253
Richards . 0.2270
S-45
5-90
5-88
5-94
5-75
6.08
6.13
Since for all the common metals the product of the atomic
weight by the specific heat for this range of temperature is in-
variably above 6.0, and averages 6.2, the conclusion is plain
that the last two figures given above must be the correct ones.
PHYSICAL PROPERTIES OF ALUMINIUM. 8 1
The high value of the specific heat of aluminium compared
with other metals, and particularly its large latent heat of
fusion, cause the metal to melt very slowly even in a very hot
fire. As seen above, over 258 calories have to be absorbed
in order to raise it to the melting point and melt it. It com-
pares with other metals as follows :
Aluminium 25^-3 calories.
Cast iron 250.0 "
Copper 162.0 "
Platinum 102.4 "
Silver 85.0
Gold 58.0 "
We can therefore deduce the interesting fact, which is amply
confirmed by observation, that having a furnace hot enough to
melt cast iron, we would find that a given weight of gold, silver
or copper would melt before the same weight of aluminium,
and even the cast-iron would not be far from melting by the
time the aluminium fused.
Electric Conductivity.
Aluminium is a very good conductor of electricity. Metal
used for electrical purposes should be of the best quality, and as
free as possible from intermingled slag or blow-holes, which
impair greatly its conductivity.
Taking the electrical conductivity of absolutely pure silver or
copper as 100, we cite the following determinations :
Silver = 100. Copper = 100.
Mattheissen. Commercial aluminium 33-76
Benoit. Annealed wire 49-7°
Watts 5610
*Lorenz 49.1 at 0°.
■< 50.1 at 100°.
'■ Unnealed wire 54.8 at 14°.
" 53-7 at 76°.
Annealed " S7.4 at 14°.
" " SS-9 at 76°.
Weiler. Best commercial metal S4-20 54.3
tC. K. McGee. Metal used
98.52 per cent. pure.
* Wied. Annalen, | 2], xiii, 422, 582 (1881).
t Trans. Am. Inst. Mining Engineers, xviii, 528 (1890).
6
82 ALUMINIUM.
The later determinations of McGee and Weiler agree very
satisfactorily. Taking 54.8 as the relative resistance at ordinary
temperatures, a wire of aluminium o.i inch in diameter and lOO
feet long would have a resistance of 0.20235 ohms.
Professor Dewar has recently investigated the electrical re-
sistance of the metals at very low temperatures. He finds with
aluminium, as with other metals, that the resistance varies
directly as the absolute temperature. The following are his
results :
Relative Electrical Resistances.
Temperature, Pure Silver. Pure Copper. Aluminium.
C° .... .... 99 per cent. 97.5 per cent.
ig.i 1588 1682 2772 2869
i.o 2583 2683
—82 1704 1738
—197 .... .... 560 506
—219 .... .... .... 325
Thermal Conductivity.
Faraday stated that he had found by a very simple experi-
ment that aluminium conducted heat better than either silver
or copper.
L. Lorenz of Copenhagen, in the Jahresbericht der Chemie,
1881, p. 94, stated that he had found it inferior to both of these
metals, and later investigations have confirmed this.
Professor Carhart, of the University of Michigan, finds that
annealed aluminium is a slightly better heat conductor than
the unannealed.
The various results are as follows :
Silver = 100, Copper = loo.
L. Lorenz 47-72 at 0°.
L. Lorenz ; . 50.00 at 100°.
Calvert and Johnson 66.5
Prof. Carhart. Annealed Metal 38.87 52.8
Prof. Carhart. Unannealed Metal 37-96 51.6
Gold is the only other metal which conducts heat better than
aluminium.
CHAPTER IV.
CHEMICAL PROPERTIES OF ALUMINIUM.
We would here repeat the remark made with regard to the
physical properties, that the properties to be recorded are those
of the purest metal unless specifically stated otherwise. How-
ever, the high grade of commercial metal differs very little in
most of its chemical properties from the absolutely pure, so
that not many reservations are necessary in applying the fol-
lowing properties to good, commercial metal:
Atomic Weight.
The most accurate determination which we have is that of
Professor Mallet, who found 27.02. For all practical purposes,
and even in analyses, it may be conveniently considered as 27.
The chemical equivalent weight is one-third of this, or 9.
Action of Air.
Deville: "Air, wet or dry, has absolutely no action on alu-
minium. No observation which has come to my knowledge
is contrary to this assertion, which may easily be proved by
any one. I have known of beams of balances, weights, plaques,
polished leaf, reflectors, etc., of the metal exposed for months
to moist air and sulphur vapors and showing no traoe of alter-
ation. We know that aluminium may be melted in the air with
impunity, therefore air and also oxygen cannot sensibly afifect
it. It resisted oxidation in the air at the highest heat I could
produce in a cupel furnace, a heat much higher than that re-
quired for the assay of gold. This experiment is interesting,
especially when the metallic button is covered with a layer of
oxide which tarnishes it, the expansion of the metal causing
(83)
§4 ALUMINIUM.
small branches to shoot from its surface, which are very bril-
liant and do not lose their lustre in spite of the oxidizing at-
mosphere. M. Wohler has also observed this property on try-
ing to melt the metal with a blowpipe. M. Peligot has profited
by it to cupel aluminium. I have seen buttons of impure
metal cupelled with lead and become very malleable.
"With pure aluminium the resistance of the metal to direct
oxidation is so considerable that at the melting point of plati-
num it is hardly appreciably touched, and does not lose its
lustre. It is well known that the more oxidizable metals take
this property away from it. But silicon itself, which is much
less oxidizable, when alloyed with it makes it burn with great
brilliancy, because there is formed a silicate of aluminium."
While the above observations are in the main true, yet it is
now well known that objects made of commercial aluminium do
after a long exposure become coated with a very thin film, which
gives the surface a "dead" appearance. The coating is very
similar in appearance to that forming on zinc under the same
circumstances. The oxidation, however, does not continue, for
the film seems to be absolutely cdntinous and to protect the
metal underneath from further oxidation. This coating can best
be removed by very dilute acid (see Mourey's receipt, p. 6o),
after which the surface can be burnished to its former brilliancy.
The action of air and rain water together also slightly cor-
rodes commercial aluminium, the sheet metal particularly
showing after several months exposure small white spots of
alumina wherever there was a speck or " piqfire." In no case,
however, is this corrosion very strong or anything like as
serious as the rusting of iron or corrosion of brass, copper, etc.
It has also been found that at a high white-heat, especially
at the heat of an electric furnace, aluminium burns with a strong
light to alumina. It is quite probable that in this case it
volatizes first, and it is the vapor which burns. During the
operation of an electric furnace a white smoke formed of invisi-
ble particles of alumina is thus formed and evolved from the
furnace. Also, in melting aluminium, even the purest, it will
CHEMICAL PROPERTIES OF ALUMINIUM. 85
be found that the surface seems bound and the aluminium
restrained from flowing freely by a minute " sl^in " which may
probably be a mixture of oxide with metal, or perhaps of oxides
of foreign metals ; but, nevertheless, it is always present and is
therefore indicative of oxidation taking place. It seems to pro-
tect the metal beneath it perfectly, so that, once formed, it gets
no thicker by continued heating.
Wohler first discovered that when aluminium was in the ex-
tremely attenuated form of a leaf it would burn brightly in air,
and burn in oxygen with a brilliant bluish-light. It is also said
that thin foil will burn in oxygen, being heated by wrapping it
around a splinter of wood, and fine wire also burns like iron
wire, but the combustion is not continuous, because the wire
fuses too quickly. The alumina resulting is quite insoluble in
acids, and as hard as corundum.
The aluminium powder, produced by pulverizing aluminium
leaf, burns brilliantly when projected into a flame, and has dis-
placed, to a large extent, magnesium powder for making a flash
Hght, because it is cheaper, gives a more strongly actinic light,
and leaves no unpleasant smoke or fumes. For this purpose it
is not used pure, but mixed with various chemicals, for the
composition of which see the chapter on "Uses of Aluminium."
Action of Water.
Deville : " Water has no action on aluminium, either at ordi-
nary temperatures or at 100°, or at a red heat bordering on the
fusing point of the metal. I boiled a fine wire in water for half
an hour and it lost not a particle in weight. The same wire was
put in a glass-tube heated to redness by an alcohol lamp and
traversed by a current of steam, but after several hours it had
not lost its polish, and had the same weight. To obtain any
sensible action it is necessary to operate at the highest heat of
a reverberatory furnace — a white heat. Even then the oxida-
tion is so feeble that it develops only in spots, producing almost
inappreciable quantities of alumina. This slight alteration and
■the analogies of the metal allow us to admit that it decomposes
86 ALUMINIUM.
water, but very feebly. If, however, metal produced by M.
Rose's method is used, which is almost unavoidably contam-
inated with slag composed of chlorides of aluminium and
sodium, the former, in presence of water, plays the part of an
acid towards aluminium, disengaging hydrogen with the forma-
tion of a subchlorhydrate of alumina, whose composition is not
known, and which is soluble in water. When the metal thus
tarnishes in water one may be sure to find chlorine in the water
on testing it with nitrate of silver."
Aluminium leaf, however, will slowly decompose water at
ioo°. Hydrogen is slowly evolved, the leaf loses its brilliancy,
becomes discolored, and, after some hours, translucent. It is
eventually entirely converted into gelatinous hydrated alumina.
A. Ditte * explains the action of water on aluminium as fol-
lows : Water can only act on aluminium by producing hydro-
gen gas and alumina, both of which deposit on the metal and
cover it with a thin, protective coating. If the conditions are
such that this coating is removed, the action becomes manifest.
Boiling, for instance, removes the hydrogen, and if chloride,
sulphate or nitrate of aluminium be present in the solution to
remove the alumina, the action goes on, a basic salt being
formed, and continues until a sub-salt is formed which is diffi-
cultly soluble or insoluble, and covers the metal with a new,
impermeable coating. Traces of these acids in the boiling
water would lead to the same result.
Action of Hydrogen Sulphide and Sulphur.
Deville : " Sulphuretted hydrogen exercises no action on
aluminium, as may be proved by leaving the metal in an
aqueous solution of the gas. In these circumstances almost all
the metals, and especially silver, blacken with great rapidity.
Sulph-hydrate of ammonia may be evaporated on an alumin-
ium leaf, leaving on the metal only a deposit of sulphur, which
the least heat drives away.
* Ann. de Chimie et de Physique [6], Vol. 20, p. 404 (i8go).
CHEMICAL PROPERTIES OF ALUMINIUM. 8/
" Aluminium may be heated in a glass tube to a red heat in
vapor of sulphur without altering the metal. This resistance is
such that in melting together polysulphide of potassium and
some aluminium containing copper or iron, the latter are at-
tacked without the aluminium being sensibly affected. Un-
happily, this method of purification may not be employed
because of the protection which aluminium exercises over
foreign metals. Under the same circumstances gold and silver
dissolve up very rapidly. However, at a high temperature I
have observed that ,it combines directly with sulphur to give
aluminium sulphide. These properties varying so much with
the temperafure from one of the special characteristics of the
metal and its alloys."
Margottet states that hydrogen sulphide is without action on
aluminium, as also are the sulphides of iron, copper, or zinc.
Aluminium is said to decompose silver sulphide, AgjS, setting
the sulphur, however, at liberty, and alloying with the silver.
In regard to its indifference to the first mentioned sulphides,
this would give inferential evidence that the reverse operation,
i. e., the action of iron, copper, or zinc on aluminium sulphide,
would be possible, as will be seen later to be apparently
established by direct experiment. As to the action of sul-
phuretted hydrogen, the author has a different experience to
quote. On passing a stream of that gas into commercial alu-
minium melted at a red heat, little explosive puffs were heard,
accompanied by a yellow light, while the dross formed on the
surface, when cooled, evolved sulphuretted hydrogen briskly
when dropped into water, and gave every indication of contain-
ing aluminium sulphide. It could not have been silicon sul-
phide, for the metal contained as large a percentage of silicon
after treatment as before. Hydrogen sulphide is also absorbed
in large quantity by molten aluminium, and mostly evolved just
as the metal is about to set. Some of the gas is entangled in
the solidifying metal, forming and fiUing numerous cavities or
blow-holes.
88 aluminium.
Sulphuric Acid.
Deville : " Sulphuric acid, diluted in the proportion most
suitable for attacking the metals which decompose water, has
no action on aluminium ; and contact with a foreign metal does
not help, as with zinc, the solution of the metal, according to
M. de la Rive. This singular fact tends to remove aluminium
considerably from those metals. To establish it better, I left
for several months some globules weighing only a few milli-
grammes in contact with the weak acid, and they showed no
visible alteration ; however, the acid gave a faint precipitate
when neutralized with aqua ammonia."
It is a fact that dilute or concentrated sulphuric acid acts
very feebly on pure aluminium in the cold, but on being heated
they both attack it, disengaging sulphurous acid gas. Impure
metal is attacked more easily than pure metal, the presence of
silicon giving rise to the formation of silicon hydride, which
communicates to the hydrogen set free a tainted odor.
Ditte* describes the action of sulphuric acid as follows : A
2.5 per cent, solution acts very slowly at first, if cold, but after
several hours the air condensed on the aluminium is removed
and the metal is slowly dissolved, evolving hydrogen. The
bubbles of hydrogen, however, protect the surface from further
attack, but anything which breaks up or removes this gaseous
envelope hastens the action of the acid. Certain solutions of
metallic chlorides which aluminium reduces act in this way.
If, for instance, we add a few drops of platinic chloride to the
above acid, platinum is reduced on the aluminium, the surface
is roughened, causing the gas to escape quicker, and the action
is much more rapid. Traces of chloride of gold, mercury or
copper have the same effect. After some time, the action of
the acid is stopped by the formation of an insoluble basic salt,
having the formula 4AI2O3.3SO3.18H2O, which deposits on the
metal and protects it from further action. Even very dilute
sulphuric acid attacks aluminium if it is prevented from cover-
ing itself with the layer of gas, as by boiling.
♦Comptes Rendus, ex., pp. 583, 782 (1890).
B.
C.
D.
98.45
99.60
9947
1.30
0.30
0.40
0.25
O.IO
0.13
CHEMICAL PROPERTIES OF ALUMINIUM. 89
It appears to the writer that similar reasoning explains why
impure aluminium is attacked more rapidly. Aluminium being
electro-positive towards the impurities it contains, it follows
that when the aluminium is at all attacked by the acid the gas
will be disengaged on the particles of the impurity, and not on
the aluminium itself ; thus the pure aluminium will never get
the benefit of the gaseous protection, and the action proceeds
rapidly.
G. A. Le Roy* tested four specimens of commercial alu-
minium, whose analysis was as follows :
A.
Aluminium 98.28
Iron 1 .5o
Silicon o. 1 2
Specimens A and B were made by the sodium process at
Nanterre ; C and D by another process, not named. The metal
was in sheets and was cut to a definite size, cleaned in soda,
washed in alcohol, dried, weighed, and then put in the acid.
Afterwards they were withdrawn, washed with water, dipped in
alcohol, dried and weighed. The results are expressed as the
weight in grammes dissolved during twelve hours from a sur-
face of one square metre :
Specific
Quality of Acid. Gravity.
Pure 1.842
Commercial i .842
Pure 1. 711
Commercial 1. 711
Pure 1.580
Pure 1.263
Pure 1.842
Commercial i .842
From these tests Le Roy concludes that it is impracticable
to think of using aluminium for the different apparatus, such as
pans, pumps, tank linings, etc., used in the manufacture or
handling of sulphuric acid.
* Le Moniteur Industriel, Oct. 29, 1891.
Degrees
Temper-
Loss in grammes per square metre in t2 hours^
Baume.
ature.
A.
B.
C.
D.
66°
I5°-20°
18.40
18.90
16.40
14.5a
66°
21.00
21.30
17.50
16.40
60"^
24.50
25.00
22.00
20.00
70°
25.80
25.70
24.60
22.40
.S.S"
19.00
18.00
17.90
16.30
30°
4.60
.. ..
2.60
340
66°
150°
240
225
150
200
66°
150°
267
250
210
220
go ALUMINIUM.
While these tests show that the aluminium is certainly dis-
solved, yet they also prove that the action is very slow. If
these acids, for instance, were contained in an aluminium vessel
I millimetre in thickness (0.04 inch), we can easily calculate
from the above figures that the concentrated acid could rest in
it cold from 60 to 90 days before eating through ; the 30° acid,
which is yet strong, would take 290 to 560 days to get through
it; while even the hot concentrated acid would not get through
in less than 5 days' constant action. We can infer that cold,
dilute acid would probably take several years in producing the
same efTect.
Nitric Acid.
Deville : " Nitric acid, weak or concentrated, does not act on
aluminium at the ordinary temperature. In boiling acid, solu-
tion takes place, but with such slowness that I had to give up
this mode of dissolving the metal in my analyses. By cooling
the solution all action ceases. On account of this property,
M. Hulot has obtained good results on substituting aluminium
for platinum in the Grove battery."
Ditte* describes the action of nitric acid similarly to that
of sulphuric. Cold 3 per cent, acid acts very slowly, 6
per cent, quicker but slower than sulphuric acid of the
same strength. When the plate becomes rough or mat by
the action, the gas escapes more freely from the surface
and the attack is more rapid. The gas evolved contains
no hydrogen, but is mostly nitrous-oxide, similarly to the
action on zinc, with a little ammonia gas. The reaction does
not stop with the formation of the neutral nitrate, but this is
acted on by the aluminium, forming a white, granular precipi-
tate of a basic salt having the formula : 6AI2O3.3N2O5.30H2O.
While cold acid thus attacks the metal very slowly, the hot
concentrated acid at 100° attacks it violently.
The amount of the action of cold nitric acid has been mea-
sured by Le Roy, Lunge, and the writer, as follows :
* Vide, p. 88.
CHEMICAL PROPERTIES OF ALUMINIUM.
91
Le Roy, pure, concentrated i5"-20°
" commercial, concentrated ! "
" " 52 per cent ! "
Lunge, pure concentrated.
" " 65 per cent. . .
" " 32 per cent. . .
Richards, pure, concentrated.
25"
B *
6 5!"
cJ rt fi
t, jj -rH
^ t/> i^ u
31-50
37-35
30.00
0.38
4.00
10.27
96.00
The figure last given includes the loss sustained in polishing
the metal to its original appearance before immersion. It re-
sults from these tests that a sheet of aluminium one millimetre
thick, if left standing in concentrated nitric acid, would sustain
constant immersion at ordinary temperatures for 3600 days
(Lunge), 43 days (Le Roy), or 14 days (Richards), if taken
out every day and polished bright.
Concerning the use of aluminium in the Grove battery, which
is not a constant battery, but only used to give a strong cur-
rent for a short time, aluminium sheet one millimetre thick
will last a long time and cost only a fraction as much as thin
platinum.
Hydrochloric Acid.
This acid attacks commercial aluminium rapidly, quicker
when hot than when cold, and the concentrated quicker than
the dilute. The very pure metal, however, is attacked slowly,
showing that, as with sulphuric acid, the galvanic action of the
impurities keeping the aluminium free from a protecting layer
•of gas, has a great influence on the resistance to acids. Gase-
ous hydrochloric acid attacks the metal even at a very low
.temperature.
The presence of silicon, particularly, increases the facility
92 ALUMINIUM.
with which the metal is attacked. When silicon is present, the
graphitic silicon remains behind as a black residue, while the
combined silicon partly forms silica and partly escapes as sili-
con hydride (SiHi), having a very disagreeable smell. When
the amount of combined silicon is small, almost all of it may
thus escape. In analyzing aluminium, this loss is prevented by
keeping the acid well oxidized by bromine water, which pre-
vents the formation of the gas. On evaporating to dryness,,
after solution, and taking up with water, the graphitoidal sili-
con remains as a black crystalline residue, while the combined
silicon has all been changed to white silica. These can be
separated by washing with hydrofluoric acid, which dissolves
the silica but leaves the silicon unattacked.
If a small amount of hydrochloric acid is present in a mix-
ture of acids, it leads the attack on the metal, and the other
acids form aluminium salts by reacting on the aluminium
chloride formed. Hydrobromic, hydriodic and hydrofluoric
acids act similarly to hydrochloric. Aluminium fluoride, how-
ever, is not so soluble in water as the other halogen salts, and
the attack by hydrofluoric acid is therefore hindered by the
formation of an insoluble coating on the aluminium when the
solution passes a certain degree of concentration.
In an experiment by the writer, best commercial rolled alu-
minium was put into cold, dilute (3 per cent.) hydrochloric
acid. It was some time before any action was observable, and
then it was very slow. It lost, after cleaning, at the rate of 5S
grammes per square metre of surface per day, which was only
a little over half as much as was dissolved by cold, concentrated
nitric acid in the same time. A piece of the same metal, how-
ever, alloyed with three per cent, of nickel was rapidly attacked
under these conditions, and over thirty times as much of it was
dissolved in a given time, thus showing strikingly the influence
of a small amount of impurity.
Organic Acids, Vinegar, Etc.
Deville : " Weak acetic acid acts on aluminium in the same
CHEMICAL PROPERTIES OF ALUMINIUM. 93
way as sulphuric acid, i. e., in an inappreciable degree or with
extreme slowness. I used for the experiment acid diluted to
the strength of strongest vinegar. M. Paul Morin left a plaque
of the metal a long time in wine which contained tartaric acid
in excess and acetic acid, and found the action on it quite in-
appreciable. The action of a mixture of acetic acid and com
mon salt in solution in pure water on pure aluminium is quite
different, for the acetic acid replaces a portion of the chlorine
existing in the sodium chloride, rendering it free. However,
this action is very slow, especially if the aluminium is pure."
" The practical results flowing from these observations deserve
to be clearly defined, because of the applications which may be
made of aluminium to culinary vessels. I have observed that
the tin so often used and which each day is put in contact with
common salt and vinegar, is attacked much more rapidly than
aluminium under the same circumstances. Although the salts
of tin are very poisonous, and their action on the economy far
from being negligible, the presence of tin in our food passes un-
perceived because of its minute quantity. Under the same
circumstances aluminium dissolves in less quantity; the acetate
of aluminium formed resolves itself on boiling into insoluble
alumina or an insoluble sub-acetate, having no more taste or
action on the body than clay itself. It is for that reason and
because it is known that the salts of the metal have no appre-
ciable action on the body, that aluminium may be considered
as an absolutely harmless metal."
The low price of aluminium has within the last two years
rendered possible this application to culinary utensils foreseen
by Deville, and has led to several investigations as to its resist-
ance to the acids and salts liable to be met with in food.
Two German pharmacists, Lubbert and Roscher, conducted
tests of this kind in 1891, but their results were only qualitative,
not quantitative, and they made the mistake of using thin
aluminium foil, which averages only o.ooi inch thick, instead
of heavier sheet. The result was that they found their thin foil
totally dissolved by two days immersion in oxalic acid (1,5
94 ALUMINIUM.
and lO per cent.), gallic acid (2 per cent.), and corrosive sub-
limate (i per cent.) ; and by four days constant immersion in
I, 5 and 10 per cent, solutions of formic, acetic, butyric, lactic,,
tartaric and citric acids, pure oleic acid, 10 per cent, solutions
of palmitic or stearic acids, in 5 per cent, solutions of carbolic
acid, 4 per cent, solution of boric acid, and in pure red wine,
white wine, coffee and tea.
It has been found, however, that because of its thinness alu-
minium foil does not resist corrosion as does the heavier sheet-
metal, and while the above results may be strictly true for foil
0.00 1 inch thick, yet ordinary sheet aluminium is not attacked
to anything like such an extent. Culinary utensils are made of
sheet at least i millimetre (0.04 inch) thick, and tests of mate-
rial of this thickness made by subsequent investigators have
given very different results.
Balland* conducted tests for several months, and found that
air, water, wine, beer, cider, coffee, milk, oil, butter, fat, urine,
saliva and damp earth have less action on aluminium than on
iron, copper, lead, zinc, or tin. Vinegar and salt together at-
tack it, but so slightly as not to prevent its use for cooking; a
sheet only lost 1.3 per cent, of its weight in vinegar, and 0.2
per cent, of its weight in a 5 per cent, salt solution after four
months' immersion.
Ruppf states that he has kept different kinds of liquid and
semi-solid food in aluminium vessels for 4 to 28 days, at the
ordinary temperature, and found the metal unaltered. The
metal used contained 0.30 per cent, of iron, 0.08 silicon and
99.66 aluminum.
Prof. Geo. Lunge, | of Zurich, has made a most careful and
systematic investigation of this subject. Assisted by Ernst
Schmid, he made the following series of tests ; ordinary com-
mercial sheet aluminum from Neuhausen was used. It ana-
lyzed :
* Comptes Rendus, 1892, Vol. 114, p. 1536.
t Chronique Industrielle, June 12, 1892.
I Zeitschrift fiir angewandte Chemie, January, 1892.
CHEMICAL PROPERTIES OF ALUMINIUM. 95
Aluminium 99.20 per cent, (by difference)
Combined silicon 0.44 "
Graphitic " o.i I "
Iron 0.25 "
Copper trace.
The sheet was i minimetre thick, and was cut into strips of
a fixed size. These were first carefully cleaned by caustic soda
and sulphuric acid, and then immersed six days in the liquids
at the ordinary temperature, each liquid being tested twice to
guard againt mistakes. The following are their results, ex-
pressed as the weight dissolved per day in milligrammes per
square metre of surface exposed :
Loss of weight per day in
milligrammes per square
Liquid. i metre of surface.
Ordinary claret 47.3
" hock 51.2
Brandy 18.0
Pure 50 per cent, alcohol 10.2
Tartaric acid, 5 per cent, solution 28.2
" '■ I " " 43.0
Acetic " S " " .64.2
" " I " " 73.0
Citric " 5 " " 35-8
" I " " 31-7
Lactic " 5 " " ■■■■■ 79-5
Butyric " 5 " " 21.8
Carbolic " 5 " " 3-8
" " 1 " •• 8.2
Boric " 4 " " 29.5
Salicylic " I4 " " 105.8
Coffee (poured hot) 8.3
Tea " 00
Beer o-o
The aluminium strips used showed outward evidences of
corrosion in only a few places ; only in the case of the salicylic
acid solution had the metal lost its bright surface and become
dull. In the case of brandy and alcohol, where the quantitative
action was very slight, the surface of the aluminium showed a
few fungus-like excresences, probably formed by alumina,
caused by accidental flaws in the sheet. In the case of a wine
96 ALUMINIUM.
rich in tannin, these spots are liable to be darkened by the in-
fluence of the trace of iron dissolved from the aluminium, form-
ing tannate of iron, but the amount thus formed is infinitesmal.
The weights dissolved are so extremely small, that it may be
calculated that a canteen holding a litre could be kept full of
the strong acetic acid for 55 years before losing half its weight.
Lunge and Schmid conclude that, " the action of coffee, tea
and beer is practically zero ; that of acids and acid liquids is
more pronounced, but in the worst case too slight to cause any
alarm whatever. Nor is there the slightest danger of any in-
jurious action on the human body by such traces of aluminium
compounds, seeing that our food contains very much more than
these ; in fact, they could not act injuriously unless quantities
hundreds of times larger were regularly entering the stomach."
The only criticism we have to make of this valuable investiga-
tion is that the solutions should have been tested hot, even
boiling, as well as cold. While it is perfectly true, as remarked
by a Washington lady, that " we hope never to have occasion
to serve our families with poisoned soups or salicylic or boracic
acid stews," yet if Lunge had made the hot-liquid tests we
should, at least, have known the worst that could possibly hap-
pen to the aluminium culinary utensils.
Happily, actual experience has settled all these questions.
An aluminium sauce-pan used in the writer's family constantly
for two years, which has been used for boiling milk, cooking
oatmeal and vegetables, stewing meats and preserving several
kinds of fruits, lost less than one-quarter ounce in the whole two
years, an average of less than 15 milligrammes per day per
square metre of surface exposed, including frequent cleaning.
I have calculated that at this rate the utensil will become a fam-
ily heirloom unless accident overtakes it, for it could stand this
rate of wear for over a century before losing half its weight.
Other experiences equally as striking could be cited, and no
better proof of the suitability of aluminium for culinary utensils
could be wished. The German Minister of War, after thorough
experiments by an army commission, has adopted aluminium
CHEMICAL PROPERTIES OF ALUMINIUM. • 9/
canteens and drinking cups for the soldiers, and entire sets of
cooking utensils for use in the officers' quarters. It is the
writer's opinion that within a short time the larger part of all
the aluminium made will be needed to supply the great demand
which will arise for these culinary utensils.
Sodium Chloride.
Common salt does not, when molten, corrode aluminium, so
that it forms a good flux to melt the metal with. It does not
possess the property, like fluorspar, of dissolving alumina, but
acts simply by its fluidity to give a clean melt.
A solution of common salt acts very feebly on aluminium.
A strip of rolled aluminium immersed in a three per cent, solu-
tion at 27° C. lost weight at the rate of 394 milligrammes per
day per square metre of surface (Hunt). The writer found a
corresponding loss of 400 milligrammes per day on sheet im-
mersed in a strong brine kept at 65° C. (150° F.) At that
rate it would take nine years' constant immersion to entirely
dissolve a sheet one millimetre thick.
When an acid is present with the salt, the action is stronger
than when either is alone. Mr. Hunt found that when two
per cent, of acetic acid was added to the salt solution previously
mentioned, the corrosion was increased to 1738 milligrammes
per day. This solution will fairly represent the extreme con-
ditions to which aluminium will be subjected in domestic culi-
nary operations, and shows that the corrosion is so slight as to
be of no practical consequence, being much less than copper,
tin-plate or iron would sufifer under similar conditions.
Sea-water corrodes aluminium slightly, but much less than
iron or steel, under similar conditions. Strips of aluminium
on the sides of a wooden sailing vessel lost less than 100 milli-
grammes per square metre of surface during six months' ex-
posure (Hunt). Messrs. Yarrow & Co., on the Thames,
having in view the building of an aluminium torpedo boat for
the French government, took two plates of aluminium stiffened
by alloying with six per cent, of copper, and after weighing
7
98 ALUMINIUM.
accurately secured them on the sides of a wooden, coppered
sailing vessel, the copper being removed to make place for
the aluminium. This ship made a voyage round the world ;
then the aluminium plates were removed, weighed, and found
to have suffered no appreciable loss. As a consequence of this
result, Messrs. Yarrow proceeded with the construction of the
boat, which is the largest vessel yet built of aluminium, having
a length of sixty feet, beam nine feet three inches and a maxi-
mum speed of twenty-two knots (twenty-five and one-half
miles) per hour.
It is to be recommended, however, that aluminium hulls in-
tended for salt water should be painted, in order to reduce any
possible corrosion to a minimum.
Organic Secretions.
These act only slightly on aluminium, the degree of corrosion
being proportioned mostly to the amount of sodium chloride
present in the secretion and its degree of acidity, or, particu-
larly, of alkalinity. The saliva acts on it so slightly that alu-
minium dental plates may be worn for many years without any
appreciable corrosion. M. Charriere, a French physician, was
the first to make a small tube of it for a person on whom trache-
otomy had been performed. He found it to remain almost
unaltered by contact with purulent matter ; after a long time a
little alumina was formed on it, hardly enough to be visible.
The use of aluminium for suture wire is also highly recom-
mended ; many instruments for physician's use are being made
of aluminium, its great advantages being lightness, incorrodibil-
ity, and being so easily cleansed, particularly by antiseptic
solutions. The tarnishing of polished aluminium articles when
constantly handled is due to the perspiration, which contains
about two per cent, of sodium chloride and about an equal
quantity of organic acids. Its action is not very strong, yet
sufficient to spoil a high polish and give a visible tarnish, as
would indeed happen to almost any other metal. If, however,
the perspiration is profuse and acts on the aluminium con-
CHEMICAL PROPERTIES OF ALUMINIUM. 99
stantly while warm, a deeper corrosion results. I have seen an
aluminium ankle-stiffener, of metal about one millimetre thick,
which was worn in the heel of a boot for about a year, and was
then eaten nearly through by the corrosion due to perspiration
a little above the ankle. The shoe lining which covered it had
served to keep it constantly in contact with the perspiration,
while the temperature may have been about 85° C. This is,
however, an extreme case, and it would be interesting to know
whether steel or very stifif leather would have lasted as long_
under the same circumstances.
Caustic Alkalies.
Deville : " Solutions of caustic potash or caustic soda ict'
with great energy on aluminium, transforming it into aluminate
of potash or soda, setting free hydrogen. However, it is not
attacked by caustic potash or soda in fusion ; one may, in fact,
drop a globule of the pure metal into melted caustic soda raised
almost to red heat in a silver vessel, without observing the
least disengagement of hydrogen. Silicon, on the contrary,
dissolves with great energy under the same circumstances. I
have employed melted caustic soda to clean siliceous alumin-
ium. The piece is dipped into the bath kept almost at red
heat. At the moment of immersion several bubbles of hydro-
gen disengage from the metallic surface, and when they have
disappeared all the silicon of the superficial layer of aluminium
has been dissolved. It only remains to wash well with water
and dip it into nitric acid, when the aluminium takes a beautiful
mat.
Mallet found that the purest aluminium resists the caustic
alkaline solution better than the commercial metal. I have-
noticed the same fact in comparing aluminium of different
degrees of purity; best commercial metal withstood the action
of cold, dilute caustic potash solution seven times better than
when it contained three per cent, of copper, and seventy times
better than when two per cent, of copper and one per cent, of
zinc were present.
lOO ALUMINIUM.
Prof. A. Stutzer,* of Bonn, finds that the metal made by the
electrolytic processes dissolves much slower than that made by
the former sodium processes. He ascribes this to the latter
metal containing nearly one per cent, of sodium. This, how-
ever, can hardly be the case, because metal made by the Deville
process rarely contained more than a trace of sodium. The true
reason must be simply the greater purity of the metal now be-
ing made by electrolysis, which averages over 99 per cent, pure
for best quality metal, while the Deville metal was rarely over
98 per cent. pure.
Ammonia.
Aqua ammonia acts slowly on aluminium, producing a little
alumina, part of which remains dissolved. Ammonia gas does •
not appear to act on the metal.
Lime Water.
This acts rapidly on aluminium at first, but the resulting
calcium aluminate is insoluble in water, and is, therefore, pre-
cipitated on the metal and quickly protects it from further
action. If this coating is scraped off the action is repeated.
Solutions of Metallic Salts.
Deville : " The action of any salt whatever on aluminium may
be easily deduced from the action of its acids on that metal. '
We may, therefore, predict that in acid solutions of sulphates
and nitrates aluminium will precipitate no metal, not even
silver, as Wohler has observed. But the hydrochloric solutions
of the same metal will be precipitated, as MM. Tissier have
shown. Likewise, in alkaline solutions, silver, lead, and metals
high in the classification of the elements are precipitated. It
may be concluded from this that to deposit aluminium on other
metals by means of the battery, it is always necessary to use
acid solutions from which hydrochloric acid, free or combined,
.should be absent. For similar reasons the alkaline solutions of
* Zeitschr. fiir angewandte Chemie, 1890, No. 23.
CHEMICAL PROPERTIES OF ALUMINIUM. lOI
the same metals cannot be employed, although they give such
good results in plating common metals with gold and silver. It
is because of these curious properties that gilding and silvering
aluminium are so difficult."
These conclusions by Deville are confirmed only when using
pure aluminium; the impure metal, containing iron, silicon, or
perhaps sodium, may produce very slight precipitates in cases
where pure aluminium would produce none. Some observers
have noted different results in some cases even when using alu-
minium free from these impurities. We will therefore take up
these cases and consider them separately.
Mercury. — * Aluminium decomposes solutions of mercuric
chloride, cyanide or nitrate, mercury separating out first, then
forming an amalgam with the aluminium which is immediately
decomposed by the water, the result being alumina and mer-
cury. From an alcoholic solution of mercurous chloride the
mercury is precipitated more quickly at a gentle heat. A solu-
tion of mercurous iodide with potassium iodide is also reduced
in like manner.
Copper. — * From solution of copper sulphate or nitrate, alu-
minium separates out copper only after two days' standing, as
either dendrites or octahedra ; from the nitrate it also precipi-
tates a green, insoluble basic salt. Copper is precipitated
immediately from a solution of cupric chloride; but slower
from the solution of copper acetate. The sulphate or nitrate
solutions behave similarly if potassium chloride is also present,
and the precipitation is complete in presence of excess of alu-
minium.
Silver. — *From a nitrate solution, feebly acid or neutral,
aluminium precipitates silver in dendrites, the separation only
beginning after six hours' standing. From an ammoniacal
solution of silver chloride or chromate, aluminium precipitates
the silver immediately as a crystalline powder. Cossa con-
firms the statement as to the nitrate solution.
Lead. — * From nitrate or acetate solution the lead is slowly
* Dr. Mierzinski.
I02 ALUMINIUM.
precipitated in crystals ; an alkaline solution of lead chromate
gives precipitates of lead and chromic oxide.
Zinc. — * An alkaline solution of zinc salt is readily decom-
posed and zinc precipitated.
Margottet states that all metallic chlorides excepting those
of potassium or sodium are reduced from solution. This state-
ment can hardly include chlorides of magnesium or lithium,
since magnesium precipitates alumina from solutions of alu-
minium salts. Alkaline or ammoniacal solutions are more
easily decomposed than acid solutions ; in alkaline solutions
the cause being the facility with which aluminates of the alka-
lies are formed.
Alkaline Chlorides. — A solution of sodium or potassium
chlorides is not appreciably affected by pure aluminium, either
cold or warm. However, rather impure aluminium which was
packed in a case with saw-dust and kept wet with sea-water for
two weeks was corroded ; whether the result would have been
the same without the presence of the saw-dust or with purer
aluminium, I cannot say.
Aluminium Salts. — It is a curious fact that a solution of alu-
minium chloride will attack aluminium, forming a basic-chloride
with evolution of hydrogen. A solution of alum does not attack
aluminium, but if sodium chloride is added it is dissolved with
evolution of hydrogen. It is interesting to note that while
neither of these salts alone attacks aluminium, the mixture of
the two does.
Fluorspar.
Fluorspar on being melted gives off a little hydroflouric acid
vapor, caused by the action of the hydroscopic moisture in it.
This vapor will attack aluminium, forming fluoride. Aside
from this slight action, the molten fluorspar has no action on
the aluminium. It has, however, the property of dissolving
a small proportion (about 2 per cent.) of alumina, and this
action causes it to be a very efficient flux, because small
* A. Cossa, Bull, de la Soc. Chim., 1870, p. 199.
CHEMICAL PROPERTIES OF ALUMINIUM. IO3
globules of aluminium are usually encrusted with a thin film
of alumina which prevents them from running together to a but-
ton. The fluorspar, by dissolving this coating and affording a
fluid mass, fluxes the separated globules together. It is often
used in connection with cryolite and common salt.
Cryolite.
Melted cryolite is a very good flux for aluminium, for the
same reason as described under fluorspar. It can, however,
dissolve over 20 per cent, of alumina, and is therefore that
much more efficient as a fluxing agent. At a temperature
above the melting point of copper it attacks the aluminium
itself, if it is put into it finely divided, but the metal en masse
is not sensibly attacked. The result of this attack must be the
formation of a sub-fluoride, possibly AIF2.
Silicates and Borates.
Neither of these classes of compounds can be used as fluxes
or slags in working aluminium, since they both rapidly corrode
the metal. Deville had little difficulty in decomposing these
salts so completely with metallic aluminium that he isolated
silicon and boron. If aluminium is melted in an ordinary
glass vessel it attacks it, setting free silicon from silica, forming
an aluminate with the alkali present and an alloy with the sili-
con set free. Aluminium melted under borax is rapidly dis-
solved, an aluminium borate being formed. It is thus seen
that the common metallurgic slags are altogether excluded
from the manufacture of aluminium, and also that it is an im-
possibility to manufacture pure aluminium direct from minerals
containing silica. The result of reducing kaolin, for instance,
would inevitably be highly siliceous aluminium, from which
there is no known method of separating out pure aluminium.
These facts also point to the importance of keeping molten
aluminium from contact with the ordinary siliceous refractory
materials in working it. Even the best quality plumbago
crucibles will increase the percentage of silicon in commercial
I04 ALUMINIUM.
aluminium at least 0.25 per cent, at one melting. Magnesia
brick linings and magnesia-lined crucibles should be used for
melting it in.
Nitre.
Deville : " Aluminium may be melted in nitre without under-
going the least alteration, the two materials rest in contact
without reacting even at a red heat, at which temperature the
salt is plainly decomposed, disengaging oxygen actively. But
if the heat is pushed to the point where nitrogen itself is disen-
gaged, there the nitre becomes potassa, a new affinity becomes
manifest, and the phenomena change. The metal then com-
bines rapidly with the potassa to give aluminate of potash.
The accompanying phenomenon of flagration often indicates a
very energetic reaction. Aluminium is continually melted with
nitre at a red heat to purify it by the oxygen disengaged, with-
out any fear of loss. But it is necessary to be very careful in
doing it in an earthen crucible. The silica of the crucible is
dissolved by the nitre, the glass thus formed is decomposed by
the aluminium, and the silicide of aluminium formed is then
very oxidizable, especially in the presence of alkalies. The
purification by nitre ought to be made in an iron crucible well
oxidized by nitre inside."
If finely divided aluminium is mixed with nitre and brought
to a red heat, the metal is oxidized with the production of a
fine blue flame. (Mierzinski.) Nitre is also used sometimes
in the composition of aluminium flash-light powders.
Alkaline Sulphates and Carbonates.
Tissier : "Only 2.65 grammes of aluminium introduced into
melted red-hot sodium sulphate (NajSOj) decomposed that
salt with such intensity that the crucible was broken into a
thousand pieces, and the door of the furnace blown to a dis-
tance. Heated to redness with alkaline carbonate, the alu-
minium was slowly oxidized at the expense of the carbonic
acid, carbon was set free, and an aluminate formed. The re-
action takes place without deflagration."
chemical properties of aluminium. i05
Metallic Oxides.
Tissier Brothers made a series of experiments on the action
of aluminium on metallic oxides. Aluminium leaf was care-
fully mixed with the oxide, the mixture placed in a small por-
celain capsule and heated in a small earthen crucible, which
served as a muffle. The results were as follows :
Manganese dioxide. — No reaction.
Zinc oxide. — No reaction even at white heat.
Ferric oxide. — By heating to white heat one equivalent of
ferric oxide and three of aluminium, the reaction took place
with detonation, and by heating sufficiently we obtained a
metallic button, well melted, containing 69.3 per cent, of iron
and 30.7 per cent, of aluminium. Its composition corresponds
very nearly to the formula AlFe. It would thus appear that
the decomposition of ferric oxide will not pass the limit where
the quantity of iron reduced is sufficient to form with the alu-
minium the alloy AlFe.
Lead oxide. — We mixed two equivalents of litharge with one
of aluminium, and heated the mixture slowly up to white heat,
when the latter reacted on the litharge with such intensity as
to produce a strong detonation. We made an experiment with
fifty grammes of litharge and 2.9 grammes of aluminium leaf,
when the crucible was broken to pieces and the doors of the
furnace blown off.
Copper oxide. — Three grammes of black oxide of copper
mixed with 1.03 grammes of aluminium detonated, producing
a strong explosion, when the heat reached whiteness.
Beketoff"* reduced baryta (BaO) with metallic aluminium in
excess, and obtained alloys of aluminium and barium contain-
ing in one case twenty-four per cent., in another thirty-three
per cent, of barium.
If any of the metallic oxides are fluxed, as by being dis-
solved in cryolite, metallic aluminium reduces them to metal at
once. Messrs. Green and Wahl have patented this method of
* Bull, de la Soc. Chimique, 1887, p. 22.
I06 ALUMINIUM.
producing pure metallic manganese, which is at present being
put into operation in Philadelphia on a commercial scale.
Miscellaneous Agents.
Phosphate of lime. — Tissier Brothers heated to whiteness a
mixture of calcium phosphate with aluminium leaf, without the
metal losing its metallic appearance or any reaction being
noted.
Hydrogen. — This gas appears to have no action on alumin-
ium, except to be dissolved in it in a moderately large quantity.
Chlorine. — Gaseous chlorine attacks the metal rapidly. Alu-
minium foil heated in an atmosphere of chlorine takes fire and
burns with a vivid light.
Bromine, iodine, act similarly to chlorine.
Fluorine. — Fluorine gas forms a thin coating of fluoride which
prevents a deeper attack. If the metal is at a dark-red heat, a
violent incandescence ensues, and the attack is very energetic.
Under the microscope the residue is seen to be globules of alu-
minium covered with uncrystallized fluoride.
Silver chloride. — Fused silver chloride is decomposed by
aluminium, the liberated silver as well as the excess of alumin-
ium being melted by the heat of the reaction.
Mercurous chloride. — If vapors of mercurous chloride are
passed through a tube in which some hot aluminium is placed,
mercury is separated out, aluminium chloride deposits in the
cooler part of the tube, and the aluminium is melted by the
heat developed.
Carbonic oxide. — Aluminium acts on this gas, forming alu-
mina and setting free carbon. Prof. Arnold proved this by
taking molten steel of a known content of carbon, and after
adding to it several per cent, of aluminium, he passed a current
of this gas through it for one hour. A sample of the metal
subsequently analyzed showed one-third more carbon than
before the treatment. This reaction is one of the causes of
the advantage of adding aluminium to molten steel, as it thus
jemoves one of the gases which form blow-holes in the cast-
ings.
CHAPTER V.
PROPERTIES AND PREPARATION OF ALUMINIUM COMPOUNDS.
In this chapter we propose to note in rather condensed form
the prominent characteristics of the various aluminium com-
pounds, with an outline of the methods by which they can be
produced, reserving for another chapter, however, the prepara-
tion of those salts which are now being manufactured on a
commercial scale for purposes of further treatment for alumin-
ium. I do not propose this as a substitute for the various
chemical treatises on this subject, but simply to add to the
completeness of this work in order that a fair understanding of
the other parts of the book may not be missed because data of
this nature are not immediately at hand. Parts of this chapter
are taken from M. Margottet's treatise on aluminium, in
Fremy's Enclycopedie Chimique.
General Considerations.
Position of aluminium in the periodic classification of the ele-
ments.— Mendeleeff places aluminium in his third family of
elements, it being preceded by boron, and followed by the rare
elements scandium, gallium, yttrium, indium, didymium, erbium
and thallium. These elements all form oxides of the same
general form, R2O3, and their other chemical compounds are
■correspondingly similar. As we have zinc, cadmium and mer-
cury as the analogues of magnesium in the second group, so we
have gallium, indium and thallium as the corresponding ana-
logues of aluminium in the third group. Unfortunately, these
elements are so rare that we are not so familiar with their prop-
erties as we could wish. We can notice, however, that as the
atomic weight increases the specific gravity and the atomic
(107 )
I08 ALUMINIUM.
volume increase also, while the compounds formed by these
metals become more easily decomposable. For instance :
Element. Atomic Weight. Specific Gravity. Atomic Volume.
Boron ii 2.5 4.5
Aluminium 27 2.7 10
Gallium 70 5.9 12
Indium 113 7.4 14
Thallium 204 11.8 17
Structure of aluminium compounds. — Aluminium has until re-
cently been regarded as a quadrivalent element, for the reason
that no compound was known whose molecule contained less than
two atoms of aluminium combined with six atoms of a mono-
valent element. Thus, the oxide was AI2O3, the chloride AhCle,,
etc. It was, therefore, supposed that in the molecule of every
aluminium compound the two atoms of aluminium were held
together by an exchange of one bond, and since each atom had
three bonds left over, it was supposed that each single alumin-
ium atom had four bonds or affinities. The composition of the
oxide and chloride were therefore represented graphically as.
follows :
r O -, Cl cl
0 = A1— A1 = 0 Cl — Al — Al — Cl
A dl
The two atoms of aluminium, having six free affinities, were
spoken of as a " double hexad-atom."
All this reasoning, however, has broken down since the dis-
covery of compounds containing only one atom of aluminium!
in a molecule, and in which the aluminium is undoudtedly tri-
valent; such are the organic salts A^CHa),, A1(C2H5)3,.
A1(C5H702)3. In the latter salt, the vapor density corresponds
to the formula given at only 45° above its melting point-
Even aluminium chloride itself has been proven to have the
formula AlCls when its vapor density is taken at a temperature
above 800°. We are therefore constrained to drop the former
PROPERTIES OF ALUMINIUM COMPOUNDS. IO9
ideas, and consider aluminium as tri-valent. The graphic
formulae given above must then be written
Cl
0 = A1 — O — Al = o Cl — Al — Cl
The tri-valency of aluminium is also required by its position
in the list of elements. Thus we have, taking the elements
immediately preceding and following it :
Atomic Weight. Valence in organic salts
Sodium 23 I
Magnesium 24 2
Aluminium 27 3
Silicon 28 4
Phosphorus 31 3
Sulphur 32 2
Chlorine 353^ i
Aluminium acts as a feeble base or a rather strong acid. As
a base it has many analogies with iron in ferric compounds.
For instance, the oxides AlzOs and FcjOg crystallize in the same
iorms, rhombohedra, with almost exactly the same fundamen-
tal angles, while the native hydrous oxides AI2O3.H2O and
Fe^Os.HjO, both crystallize in the orthorhombic system with
very similar angles and cleavages. As an acid, it forms com-
pounds analogous to ferric and chromic acids. For instance :
Aluminate of iron ^. FeAl^O,.
Ferrate " " FeFejOj.
Chromate " " FeCr^O^.
These all crystallize in isometric octahedra, and are in every
respect very similar minerals. The salts in which aluminium
acts as an acid are called aluminates. They may be written
as salts of aluminic acid, HjAljO^, but there are other alumin-
ates known having a smaller proportion of alumina, and it is
much more convenient to express the composition of all these
aluminates by the dualistic method. Thus, there are known to
exist (see Bayer's method of treating bauxite, next chapter.)
I lO ALUMINIUM.
Al203.Na20.
AljOj.zNa^O.
Al,03.3Na,0.
AljOs.eNa^O.
the writing of which formulae by the rationalistic method would
be very cumbersome.
The normal or neutral salts of aluminium as a base may be
regarded as the acid with its hydrogen replaced by alumin-
ium. Thus :
Acid. Salt.
3HCI AlCls
3QH,0, AlCQHsO,),
3H,S0t A1,(S0J3
HaPjO^ AIP2O4
Aluminium, however, has a great tendency to form basic
salts when these neutral salts are put in contact with an excess
of aluminium or alumina. It is most convenient to write the
formulae of these by the dualistic method. Thus we have :
Normal sulphate, AI2O3.3SO3.16HJO. Basic sulphate, 2AI2O3.SO3.10H2O.
Normal acetate, AI2O3.6C2H2O. Basic acetate, Al20s.2C2H.^0.2H20.
While the writer has no intention of going back to the
duaHstic theories which such formulae were first used to repre-
sent, yet he takes the liberty of using these formulas to represent
the empirical composition of these salts, because of their con-
venience, and without attaching to them any theories as to the
internal structure of the molecules.
General methods of formation and properties. — Hydrated alu-
mina, which has not been too strongly heated, dissolves in
strong acids, forming salts which are mostly soluble in water.
In the feebler acids and in all organic acids it is completely in-
soluble. The salts of these latter acids are formed best by de-
composing solution of aluminium sulphate with the barium or
lead salt of the acid in question. Most aluminium salts are
soluble in water and rather difficult to crystallize : the few in-
soluble salts are white, gelatinous, and similar to the hydrate
PROPERTIES OF ALUMINIUM COMPOUNDS. Ill
in appearance. In the neutral salts the acid is loosely held,
for their solution strongly reddens litmus paper and their action
is as if part of the acid were free in the salt. For instance, a
solution of alum attacks iron giving ofi hydrogen, a soluble
basic salt of aluminium being formed as well as sulphate of
iron. The neutral salts of volatile acids give ofif acid simply by
boiling their solutions, basic salts being formed. An aqueous
solution of aluminium chloride loses its acid almost completely
on evaporation. Gentle ignition is sufficient in most cases to
completely decompose aluminium salts. Hydrated alumina
dissolves easily in caustic alkali, forming soluble aluminates ;
with baryta two aluminates are known, one soluble, the other
not ; all other known aluminates are insoluble.
Chemical reactions. — Neutral solutions of aluminium salts
react as follows with the common reagents :
Hydrogen sulphide produces no precipitate.
Ammonium sulphide precipitates aluminium hydrate with
separation of free sulphur.
Caustic potash or soda precipitates aluminium hydrate, solu-
ble in excess.
Aqua ammonia precipitates aluminium hydrate insoluble in
excess, especially in presence of ammoniacal salts.
Alkaline carbonates precipitate aluminium hydrate insoluble
in excess.
Sodium phosphate precipitates white gelatinous aluminium
phosphate, easily soluble in acids or alkalies.
Before the blowpipe most aluminium compounds are infusible
or are quickly converted into infusible alumina. In the light-
colored, infusible compounds, the aluminium may be recognized
by giving a beautiful, enamel-like blue color (Thenard's blue)
when moistened with dilute solution of cobalt nitrate and
ignited in a pure oxidizing flame. Light-colored fusible com-
pounds will also give the same reaction, but in them the ab-
sence of silica, boric and phosphoric acids must be proven by
other tests before the presence of aluminium can be asserted
with certainty.
i i 2 aluminium.
Aluminium Oxide.
Commonly called alumina. Composition Al^Oj, and contains
52.95 per cent, of aluminium when perfectly pure. Colorless
corundum is a natural pure alumina, in which state it is infusible
at ordinary furnace heats, insoluble in acids, has a specific
gravity of 4, and is almost as hard as the diamond. To get
this into solution it must be first fused with potassium hydrate
or bisulphate. The alumina made by igniting aluminium hy-
drate or sulphate is a white powder, easily soluble in acids if
the ignition has been gentle, but becoming almost insoluble if
the heat has been raised to whiteness. The specific gravity of
this ignited alumina also varies with the temperature to which
it has been raised; if simply to red heat, it is 3.75 ; if to bright
redness, 3.8; and if to whiteness, 3.9. In the last case it ac-
quires almost .the hardness of corundum. It can be melted to a
clear, limpid liquid in the oxyhydrogen blow-pipe ; after cool-
ing it forms a clear glass, often crystallized. Small artificial
crystals of alumina, exactly similar to the natural ones, have
been obtained by dissolving powdered alumina in fused boric
oxide and then volatilizing the latter by an intense heat.
Fluorine gas acts energetically on powdered alumina. As
soon as it comes in contact, the whole mass becomes incandes-
cent, forming a fluoride and disengaging oxygen. The reaction
A\A + 6F = 2AIF3 + 30.
disengages i,ioo calories of heat per kilogramme of fluorine
acting. Gaseous chlorine does not act on it even at redness,
but if carbon is present at the same time aluminium chloride is
formed. Similarly, although neither carbon nor sulphur, alone
or mixed together, acts on alumina, carbon bisulphide converts
it into aluminium sulphide.
The preparation of alumina for commercial purposes is de-
scribed at length in the next chapter.
properties of aluminium compounds. ii 3
Aluminium Hydrates.
There are three natural hydrates of aluminium, which may-
be briefly described as follows :
Diaspore, formula AI2O3.H2O or Al202.(OH)j, containing 85
per cent, of alumina, occurs in crystalline masses as hard as
quartz, with a specific gravity of 3.4. Bauxite, approximately
of the formula AI2O3.2H2O or Al20.(OH)4, with the aluminium
replaced by variable quantities of iron. If perfectly pure, it
would contain 74 per cent, of alumina. Hydrochloric acid re-
removes from it only the iron ; heated with moderately dilute
sulphuric acid it gives up its alumina; a concentrated alkaline
solution also dissolves the alumina. Calcined with sodium
carbonate it forms sodium aluminate without melting. Gibbsite,
formula AI2O3.3H2O or Al2(OH)6, containing, when pure sixty-
five per cent, of alumina, is a mineral generally stalactitic,
white, and with a specific gravity of 2.4. It loses two-thirds of
its water at 300° and the rest at redness.
The artificial hydrates are of two kinds, the soluble and in-
soluble modifications. The latter is the common hydrate, such
as is obtained by adding ammonia to a solution containing alu-
minium. The precipitate is pure white, very voluminous, and
can be washed free from the salts with which it was precipi-
tated only with great difficulty. Its composition is Al2(OH)6,
corresponding to the mineral gibbsite. It is insoluble in water,
but easily soluble in dilute acids or alkali solutions. It dis-
solves in small quantity in ammonia, but the presence of am-
monia salts counteracts this action. When dissolved in caustic
potash or soda the addition of ammoniacal salts reprecipitates it.
It loses its water on heating, in the same manner as gibbsite.
Many other properties of this hydrate, and its manufacture on
a large scale, are given in the next chapter. The soluble modi-
fication can only be made by complicated processes, too long
to be described here, and is principally of use in the dyeing
industries ; a full description can be found in any good chemi-
cal dictionary.
8
114 aluminium.
Aluminates.
Potassium aluminate. — Formula KjAljO^, crystallizes with
three molecules of water, the crystals containing forty per cent,
alumina, 37.5 per cent, potassa and 21.5 per cent, of water. It
is formed when precipitated alumina is dissolved in caustic
potash, or by melting together alumina and caustic potash in a
silver dish and dissolving in water. If the solution is evapo-
rated in vacuo, brilliant hard crystals separate out. They are
soluble in water but insoluble in alcohol.
Sodium aluminate has not been obtained crystallized. Ob-
tained in solution by dissolving alumina in caustic soda or by
fusing alumina with caustic soda or sodium carbonate and dis-
solving in water. If single equivalents of carbonate of soda
and alumina are used, the aluminate seems to have the com-
position NajAljOi) if an excess of soda is used, the solution
appears to contain Al2(0Na)e, or AljOj.sNajO. Dr. Bayer
thinks that Al203.2Na20 and Al203.6Na20 are also possible in
solution. If a solution of sodium aluminate is concentrated to
20° or 30° B., alumina separates out; if carbonic acid gas is
passed through it, aluminium hydrate is precipitated. For a
description of its' manufacture on a large scale, see next
chapter.
Barium aluminate. — Formula BaAl^Oi. Deville prepared it
by calcining a mixture of nitrate or carbonate of barium with •
an excess of alumina, or by precipitating sulphate of aluminium
in solution by baryta water in excess. The aluminate is solu-
ble in about ten times its weight of water and crystallizes out
on addition of alcohol. The crystals contain four molecules of
water. Gaudin obtained it by passing steam over a mixture of
alumina and barium chloride, or of alumina, barium sulphate,
and carbon, at a red heat. Tedesco claimed that by heating
to redness a mixture of alumina, barium sulphate, and carbon,
barium aluminate was extracted from the residue by washing
with water. He utilized this reaction further by adding solu-
tion of alkaline sulphate, barium sulphate being precipitated
PROPERTIES OF ALUMINIUM COMPOUNDS. II5
(which was used over), while alkaline aluminate remained in
solution.
Calcium, aluminate. — Lime water precipitates completely a
solution of potassium or sodium aluminate, insoluble gelatinous
calcium aluminate being formed, of the formula A]2(06Ca3) or'
AljOs.sCaO. At a red heat it melts to a glass, which, treated
after cooling with boiling solution of boric acid, affords a com-
pound appearing to contain aAljOj-SCaO. (Tissier.) Lime
water is also completely precipitated by hydrated alumina, the-^^
compound formed having the composition CaAljOi or AI2O3.--
CaO. Also, by igniting at a high temperature an intimate
mixture of equal parts of alumina and chalk, Deville obtained^
a fused compound corresponding to the formfila CaAljO^.
Zinc aluminate occurs in nature as the mineral Gahnit^,
formula ZnALOi. Berzelius has remarked that when a solution
of zinc oxide in ammonia and a saturated solution of alumina
in caustic potash are mixed, a compound of the two oxides is
precipitated, which is redissolved by an excess of either alkali.
Copper aluminate. — On precipitating a dilute solution of
sodium aluminate with an ammoniacal solution of copper sul-
phate, the clear solution remaining contained neither copper
nor aluminium. Whether the precipitate contained these com-
bined as an aluminate I did not determine.
Magnesium aluminate occurs in nature as Spinel; iron
aluminate as Hercynite; beryllium aluminate as Chrysoberyl.
The first mentioned has been lately proven to exist in small
quantities in crystallized blast-furnace slags.* Ebelman has
also prepared it in small crystals by dissolving alumina and
magnesia in fused boric oxide and driving off some of the
solvent by intense heat.
Aluminium Chloride.
Formula AICI3, contains 20.2 per cent, of aluminium. The
commercial chloride is often yellow or even red from the pres-
ence of iron, but the pure salt is quite white. It absorbs water
* P. W. Shimer. Journal Am. Chemical Soc, 1894, p. 501.
Il6 ALUMINIUM.
very rapidly from the air. It usually sublimes without melting,
■especially when in small quantity, but if a large mass is rapidly
ieated, it may melt and even boil, but its melting point is very
close to its boiling point. Friedel and Crafts have determined
the melting point as 178°, boiling point 183°. When sublimed
it deposits in brilliant, hexagonal crystals. A current of steam
rapidly decomposes it into alumina and hydrochloric acid.
Oxygen disengages chlorine from it at redness, but decomposes
it incompletely. Potassium or sodium decomposes it ex-
plosively, the action commencing below redness. Anhydrous
sulphuric acid converts it into aluminium sulphate. Alumin-
ium chloride combines with many other chlorides, forming the
double salts.
On dissolving this salt in water, or by dissolving alumina in
hydrochloric acid, a solution is obtained which on evaporation
deposits crystals having the formula AICI3.6H2O. If these
crystals are heated, they decompose, losing both water and
acid and leaving alumina. Thus it is not possible to obtain
anhydrous aluminium chloride by evaporating its solution, and
the anhydrous salt must be made by other methods, detailed at
length in the next chapter.
Aluminium-Sodium Chloride.
formula AlClj.NaCl contains 14 per cent, of aluminium.
The commercial salt is often yellow or brown from the presence
,of ferric chloride, but the pure salt is perfectly white. Its melt-
ing point has been generally stated to be 180°, but Mr. Baker,
<chemis.t for the Aluminium Company of London, states that
-when .the absolutely pure salt is warmed it melts at 125° to
130°. Xhat chemists should for thirty years have made an
.error of this magnitude seems almost incredible, and it would
be satisfactory if Mr. Baker would advance some further in-
formation than the bare statement above. This salt volatilizes
at a red heat without decomposition. It is less deliquescent in
the air .than aluminium chloride, and for this reason is much
icagier .to handle on a large scale. It is recently stated that the
PROPERTIES OF ALUMINIUM COMPOUNDS. 11/
absolutely pure salt deteriorates less than the impure salt in the
air, and the inference is drawn that perhaps the greater deli-
quescence of the impure salt is due to the iron chlorides pres-
ent. Its solution in water behaves similarly to that of alumin-
ium chloride ; it cannot be evaporated to dryness without
decomposition, the residue consisting of alumina and sodiun:i
chloride.
The manufacture of this double salt on a large scale is de-
scribed in the next chapter. It may be prepared in the labora-
tory by melting a mixture of the two component salts in the
proper proportions. A similar salt with potassium chloride
may be prepared by exactly analogous reactions.
Aluminium-Phosphorus Chloride.
Formula 2AICI3.PCI5, contains 9 per cent, of aluminium. It
is a white salt, easily fusible, volatilizes only about 400° and
sublimes slowly, fumes in the air and is decomposed by water.
Produced by heating the two chlorides together or by passing
vapor of phosphorus perchloride over alumina heated to redness.
Aluminium-Sulphur Chloride.
Formula 2AICI3.SCI4, contains 12.2 per cent, of aluminium.
It forms a yellow crystalline mass, fuses at 100°, may be dis-
tilled without change, and is decomposed by water. May be
obtained by distilling a mixture of aluminium chloride and
ordinary sulphur chloride, SClj.
Aluminium-Selenium Chloride.
Formula 2AlCl3.SeCl4. Obtained by heating the separate
chlorides together in a sealed tube, when on careful distillation
the less volatile double chloride remains. It is a yellow mass,
melting at 100° and decomposed by water.
Aluminium-Ammonium Chloride.
Formula 2AICI3.3NH3. Solid aluminium chloride absorbs
ammonia in large quantity, the heat developed liquefying the
Il8 ALUMINIUM.
resulting compound. It may be sublimed in a current of
hydrogen, but loses ammonia thereby and becomes 2AICI3.NH3.
Aluminium-Chlor-sulphydride.
Formed by subliming aluminium chloride in a current of
hydrogen sulphide. A current of hydrogen removes the ex-
cess of the gas used, leaving on sublimation fine colorless
crystals. In air it deliquesces rapidly and loses hydrogen
sulphide.
Aluminium-Chlor-phosphydride.
Apparently of the formula 6AICI3.PH3. If phosphuretted
hydrogen is passed over cold aluminium chloride very little is
absorbed, but at its subliming point it absorbs a large quantity,
the combination subliming and depositing in crystals. It is
decomposed by water or ammonium hydrate, disengaging
hydrogen phosphide.
Aluminium Bromide.
Formula AlBrg, containing lo.i per cent, of aluminium. It
is colorless, crystalline, melts at 93° to a clear fluid which boils
at 260°. It is still more deliquescent than aluminium chloride.
At a red heat in contact with dry oxygen, it evolves bromine
and forms alumina ; it is also decomposed slowly by the oxy-
gen of the air. It dissolves easily in carbon bi-sulphide, the
solution fuming strongly in the air. It reacts violently with
water, the solution on evaporation depositing the compound
AlBr3.6H20. The same result is attained by dissolving alumina
in hydrobromic acid and evaporating. This hydrated chloride
is decomposed by heat, leaving alumina. The specific gravity
of solid aluminium bromide is 2.5.
This compound is obtained by heating aluminium and bro-
mine together to redness, or by passing bromine vapor over a
mixture of alumina and carbon at bright redness.
Aluminium Iodide.
Formula AII3, containing 6.6 per cent, of aluminium. This
PROPERTIES OF ALUMINIUM COMPOUNDS. II 9
compound is a white solid, fusible at 125°, and boils at 350°.
It dissolves easily in carbon bisulphide, the warm saturated
solution depositing it in crystals on cooling. It dissolves also
in alcohol and ether. Its behavior towards water is exactly
analogous to that of aluminium bromide. It is prepared by
heating iodine and aluminium together, with special precau-
tions to avoid explosion.
Aluminium Fluoride.
Formula AIF3, containing 32.7 per cent, of aluminium. It
is sometimes obtained in crystals which are colorless and
slightly phosphorescent. They are insoluble in acids, even in
boiling sulphuric, and boiling solution of potash scarcely at-
tacks them ; they can only be decomposed by fusion with
sodium carbonate at a bright red heat. Melted with boric
acid, aluminium fluoride forms crystals of aluminium borate.
L. Grabau describes the aluminium fluoride which he obtains
in his process as being a white powder, unalterable in air,
unaffected by keeping, insoluble in water, infusible at redness,
but volatilizing at a higher temperature.
Deville first produced this compound by acting on alumin-
ium with silicon fluoride at a red heat. He afterwards obtained
it by moistening pure calcined alumina with hydrofluoric
acid, drying and introducing into a tube made of gas carbon,
protected by a refractory envelope. The tube was heated to
bright redness, a current of hydrogen passing through mean-
while to facilitate the volatilization of the fluoride. Brunner
demonstrated that aluminium fluoride is formed and volatilized
when hydrofluoric acid gas is passed over red-hot alumina.
Finally, if a mixture of fluorspar and alumina is placed in car-
bon boats, put into a carbon tube, suitably protected, heated to
whiteness and gaseous hydrofluoric acid passed over it, alu-
minium fluoride will volatilize and condense in the cooler part
of the tube in fine cubical crystals, while calcium fluoride re-
mains in the boats.
i20 aluminium.
Aluminium Fluorhydrate.
When calcined alumina or kaolin is treated with hydrofluoric
acid, alumina being in excess, soluble fluorhydrate of alumin-
ium is formed, which deposits on evaporating the solution. It
has the formula 2AIF3.5H2O, and easily loses its water when
heated.
Aluminium-Hydrogen Fluoride.
If to a strongly acid solution of alumina in hydrofluoric acid
alcohol is added, an oily material separates out and crystallizes,
having the formula 3AIF3.2HF.5H2O. If the acid solution is
simply evaporated, acid fumes escape and a crystalline mass
remains which, washed with boiling water and dried, has the
formula 4AIF3.HF.10H2O. On heating these compounds to
400° or 500° in a current of hydrogen, pure amorphous alu-
minium fluoride remains. The acid solution of alumina first
used seems to contain an acid of the composition AIF3.3HF,
which is capable of forming salts with other bases. Thus, if
this solution is neutralized with a solution of soda, a precipitate
of artificial cryolite, AlFs.sNaF, falls. The similar potash
compound is formed in the same way.
Aluminium-Sodium Fluoride.
Formula AlFs.sNaF, containing 12.85 P^r cent, of aluminium,
occurs native as cryolite, a white mineral with a waxy appear-
ance, as hard as calcite, specific gravity 2.9, melting below
redness and on cooling looking like opaque, milky glass. If
kept melted in moist air, or in a current of steam, it loses
hydrofluoric acid and sodium fluoride and leaves a residue of
pure alumina. When melted it is decomposable by an electric
current or by sodium or magnesium. It is insoluble in water,
unattacked by hydrochloric but decomposed by hot sulphuric
acid. The native mineral is contaminated with ferrous carbon-
ate, silica, phosphoric and vanadic acids. An extended de-
scription of its utilization, manufacture, etc., will be found in
the next chapter.
PROPERTIES OF ALUMINIUM COMPOUNDS. 121
A native compound having the formula sAlFj.jNaF is snow-
white, very similar to cryolite in appearance and properties,
except that it crystallizes in a different form and is more
fusible. It is called Chiolite. The mineral Pachnolite is also
similar, except that part of the sodium is displaced by calcium.
Aluminium Sulphide.
Formula AI2S3, containing 36 per cent, of aluminium. The
pure salt is light yellow in color and melts at a high tempera-
ture. In damp air it swells up and disengages hydrogen sul-
phide, forming a grayish white powder ; it decomposes water
very actively, forming hydrogen sulphide and ordinary gela-
tinous aluminium hydrate. Steam decomposes it easily, at red
heat forming amorphous alumina, which is translucent and very
hard. Gaseous hydrochloric acid transforms it into aluminium
chloride. Elements having a strong affinity for sulphur reduce
it, setting free aluminium, but it is doubtful if hydrogen or
carburetted hydrogen has this efifect.
It may be formed by throwing sulphur into red-hot alumin-
ium, or by passing sulphur vapor over red-hot aluminium.
Traces only of aluminium sulphide are formed by passing
hydrogen sulphide over ignited alumina, but carbon-bisulphide
vapor readily produces this reaction. For details of its forma-
tion see next chapter.
Double sulphides of aluminium and sodium or potassium,,
similar in composition to the double chlorides, may be made
by melting the two sulphides together, or, more easily, by add-
ing sodium or potassium carbonate to the ignited alumina
which is in process of conversion into sulphide. These salts
are easily fusible and nearly unchangeable in the air, but a
more detailed description of them is wanting. They are said
to be quite suitable for electrolytic decomposition. (See
Bucherer's electrolytic process.)
Aluminium sulphide has recently come into use in chemical
laboratories as a very convenient means of generating hydrogen
sulphide. A London chemical firm manufactures it by stirring
122 ALUMINIUM.
aluminium into molten sulphide of lead ; the lead separating
out sinks to the bottom, while the aluminium sulphide floats.
The sulphide is sold at $0.6o per pound, and is said to gen-
erate the gas as cheaply as by the ordinary methods.
Aluminium Selenide.
When aluminium is heated in selenium vapor, the two ele-
ments combine with incandescence, producing a black powder.
In the air this powder evolves the odor of hydrogen selenide ;
in contact with water it disengages that gas abundantly, and
furnishes a red deposit of selenium along with aluminium
hydrate. When a solution of an aluminium salt is treated with
an alkaline poly-selenide, a flesh-colored precipitate falls, the
composition of which is not known, which is decomposed at
redness, leaving aluminium.
Aluminium Borides.
AIB2, containing 55.1 per cent, of aluminium, was first ob-
tained by Deville and Wohler by heating boron in contact with
aluminium, or by reducing boric acid with the latter metal, the
action not being long continued. Also, if a current of boron
trichloride with carbonic oxide is passed over aluminium in
boats in a tube heated to redness, aluminium chloride volatil-
izes and there remains in the boats a crystalline mass, cleav-
able, and covered with large hexagonal plates of a high metal- '
lie lustre. To remove the aluminium present in excess, the
mass is treated with hydrochloric acid and then with caustic
soda. The final residue is composed of hexagonal tablets, very
thin but perfectly opaque, of about the color of copper. These
crystals do not burn in the air, even if heated to redness, but
their color changes to dark-gray. They burn in a current of
chlorine, giving chlorides of the two elements contained in
them. They dissolve slowly in concentrated hydrochloric acid
or in solution of caustic soda ; nitric acid, moderately concen-
trated, attacks them quickly.
AlBs, containing 45 per cent, of aluminium, has been ob-
PROPERTIES OF ALUMINIUM COMPOUNDS. 1 23
tained by Hampe by heating aluminium with boric acid for
three hours at a high temperature, carbon being carefully kept
away. On cooling very slowly, the upper part of the fusion is
composed of aluminium borate, the centre is of very hard
alumina containing a few black crystals of aluminium boride,
while at the bottom is a button of aluminium also containing
these crystals. To free these crystals, the aluminium is dis-
solved by hydrochloric acid. These crystals are the compound
sought for, and contain no other impurity than a little alumina,
which can be removed by boihng sulphuric acid. These puri-
fied crystals are black, but are thin enough to show a dark-red
by transmitted light. Their specific gravity is 2.5, they are
harder than corundum, but are scratched by the diamond.
Oxygen has no action on them at a high temperature, solution
of caustic potash or hydrochloric acid does not attack them,
boiling sulphuric acid has scarcely any action, but they dissolve
completely in warm, concentrated nitric acid.
If the operation by which this product is made is conducted
in the presence of carbon, the compound formed contains less
aluminium and also some carbon. Its composition corresponds
to the formula Al3C2B«, containing about 12 per cent, of alu-
minium and 3.75 per cent, of carbon. The crystals of this
compound are yellow and as brilliant as the diamond. Their
specific gravity is 2.6, hardness between that of corundum and
the diamond. They are not attacked by oxygen, even at a
high temperature; hot hydrochloric or sulphuric acid attacks
them only superficially, concentrated nitric acid dissolves them
slowly but completely. They resist boiling solution of caustic
potash or fused nitre, but take fire in fused caustic potash or
chromate of lead.
Aluminium and Carbon.
Deviile stated that he was unable to combine carbon with
aluminium. On decomposing carbon tetrachloride by aluniin-
ium, ordinary carbon was formed, while the aluminium remain-
ing was unchanged. The Cowles Company obtain in their
124 ALUMINIUM'.
electric furnace, when reducing a mixture of alumina and car-
bon alone, a yellow, crystalline substance which was exhibited
by Dr. T. Sterry Hunt,* as an alloy of aluminium and carbon,,
but that this is the case is not yet accepted as certain.
On dissolving impure aluminium in solution of caustic pot-
ash, a black residue was obtained which behaved, when filtered'
out and dried, partly like amorphous carbon. I have heard
it stated that molten aluminium does not dissolve appreciable-
quantities of carbon, and that its properties are affected con-
siderably thereby; but I am not able to give any further light
on the subject than the above experiment, which seemed to-
show considerable carbon in an impure metal. This is a sub-
ject which needs thorough investigation.
Since the observation just given was made, in 1890, the fact
that this residue does contain amorphous carbon has been es-
tablished by Le Verrier (see p. 57), who has also confirmed
Hunt's statements as to an aluminium carbide. Le Verrier
states I that up to his own experiments this compound was
unknown, but he must have been ignorant of Hunt's observa-
tions. The method used by Le Verrier was as follows: Little
boats of carbon were filled with aluminium, put into a carbon
tube through which a current of hydrogen was passed, and
heated in the electric furnace. After cooling, the aluminium
was of a grey color, and on breaking it was seen to be strewn
with brilliant fine-yellow crystals. To separate these out, the
aluminium is dissolved by concentrated hydrochloric acid, sur-
rounding the vessel with ice to keep the temperature low. The
residue is washed with ice-cold water. This whole operation
must be conducted as quickly as possible, since the carbide is
attacked by water.
The carbide thus prepared has a specific gravity, taken in
benzine, of 2.36. It is decomposed in the highest heat of an
electric furnace, attacked by chlorine at a red-heat, but only
♦Halifax Meeting, Am. Ins. Mining Engineers, Sept. i6, 1885.
tComptes Rendus, July, 1894, p. 16.
PROPERTIES OF ALUMINIUM COMPOUNDS. 125
superficially by oxygen, since the layer of alumina formed pro-
tects the part underneath. Violently attacked by sulphur at
that temperature, also by permanganate of potassium, bichro-
mate of potassium, chromic acid and oxide of lead ; potassium
chlorate has no action. Caustic potash in fusion attacks it very
energetically at about 300°. It slowly decomposes water in
the cold with a very curious result, namely, the formation of
jnethane gas, according to the reaction :
QAl^ + 12H2O = aCH, -f- 4A1(0H)3.
An analysis of these crystals gave the following result :
Aluminium. Carbon.
7448 23.5
7.5.12 24.2
74-7 24.7
74.9 24.8
75-7
(Required by the formula AI4C3.)
75.4 24.6
Aluminium Nitride.
Formula AIN, containing 66 per cent, of aluminium, is
iormed when aluminium is heated in a carbon crucible to a
high temperature. Mallet* obtained it unexpectedly when
heating aluminium with dry sodium carbonate at a high heat,
lor several hours, in a carbon crucible. The aluminium is par-
tially transformed into alumina, some sodium vaporizes, and
some carbon is deposited. After cooling, there are found on
the surface of the button little yellow crystals and amorphous
drops, to recover which the whole is treated with very dilute
hydrochloric acid. This product has the composition AIN.
"Calcined in the air it slowly loses nitrogen and forms alumina.
It decomposes in moist air, loses its transparency, becomes a
lighter yellow, and finally only alumina remains, the nitrogen
*Ann. der Chemie u. Pharmacie, 186, p. 155.
126 ALUMINIUM.
having formed ammonia. Melted with caustic potash it dis-
engages ammonia and forms potassium aluminate.
Aluminium Sulphate.
Anhydrous. — The salt obtained by drying hydrated alumin-
ium sulphate at a gentle heat has the formula Al2(S04)3, con-
taining 15.8 per cent, of aluminium, and of a specific gravity
of 2.67. By heating this salt several minutes over a Bunsen
burner it loses almost all its acid, leaving alumina. Hydrogen
likewise decomposes it at redness, forming water and sulphur
dioxide and leaving alumina with hardly a trace of acid.
Melted with sulphur, Violi states that it is transformed into
aluminium sulphide, evolving sulphurous acid gas.* Hot
hydrochloric acid in excess partly converts it into aluminium
chloride.
Hydrated. — This is the ordinary aluminium sulphate; its
formula is Al2(S04)3.i6H20, and it contains 8.0 per cent, of
aluminium, equal to 14.5 per cent, of alumina, and 47 per cent,
of water. The pure salt is not hygroscopic. In the presence
of impurities the amount of water increases to 18 H2O and the
salt becomes hygroscopic. It has a white, crystalline appear-
ance, and tastes like alum. It dissolves freely in water, from
which it crystallizes out at ordinary temperatures with the
above formula ; crystallized out at a low temperature it retains
27H2O, or one-half as much again. Water dissolves one-half
its weight of this salt, the solution reacting strongly acid ; it is
almost insoluble in alcohol. At a gentle heat it melts in its
water of crystallization, then puffs up and leaves a porous mass
of anhydrous sulphate which is soluble with difficulty in water.
If heated to redness it leaves only alumina. The salt with
16H2O has a specific gravity of 1.76; it is the salt found in
fibrous masses in solfataras, its mineralogical name being Halo-
trichite. A hydrated sulphate with 10H2O is formed and pre-
cipitated when alcohol is added to an aqueous solution of alu-
* Berichte der Deutschen Chemischen Gesellschaft, X, 293.
PROPERTIES OF ALUMINIUM COMPOUNDS. 12/
minium sulphate. On heating it acts similarly to the other
hydrated sulphates.
Basic. — On precipitating a solution of aluminium sulphate
with alkaline hydrate or carbonate, a series of basic salts are
formed. On precipitating with ammonia, the compound formed
has the formula AljO3.SO3.9HjO, corresponding to the mineral
Aluminite. If the ammonia is in insufficient quantity to en-
tirely precipitate the solution, a precipitate is very slowly
formed having the formula 3AI2O3.2SO3.20H2O. On precipitat-
ing a cold solution of alum by alkaline carbonate not in excess,
a precipitate is very slowly formed having the formula 2A1203.-
SO3.12H2O. If a very dilute solution of acetate of alumina is
precipitated by adding potassium sulphate, a compound de-
posits very slowly having the formula 2AI2O3.SO3.10H2O. Na-
tive minerals are met with of analogous composition to these
precipitates: Felsobanyte, 2AI2O3.SO3.10H2O ; Paraluminite,
2AI2O3.SO3.ISH2O. By heating a concentrated solution of alu-
minium sulphate with aluminium hydrate, and filtering cold,
the solution deposits on further cooling a gummy mass having
the formula Al203.2S03.;irH20. On washing with water it de-
posits a basic salt having the formula AI2O3.SO3. By letting
stand a very dilute solution of sulphuric acid completely satu-
rated with aluminium hydrate, Rammelsberg obtained trans-
parent crystals having the formula 3AI2O3.4SO3.30H2O. On
boiling a solution of aluminium sulphate with zinc, Debray
obtained a granular precipitate having the formula 5AI2O3.3SO3.-
20H2O. By leaving zinc a long time in a cold solution of alu-
minium sulphate, a gelatinous precipitate was obtained having
the formula 4AI2O3.3SO3.36H2O ; the same compound was
formed if the zinc was replaced by calcium carbonate.
The manufacture of aluminium sulphate from clay, aluminous
earths, cryolite, bauxite, etc. , is carried on industrially on a
very large scale ; descriptions of the processes used may be
found in any work on industrial chemistry — they are too foreign
to metallurgical purposes to be treated of here.
128 aluminium.
Alums.
Under this name are included a number of double salts con-
taining water, crystallizing in octahedra and having the general
formula R2S04.R2(S04)3.24H20, in which the first R may be
potassium, sodium, rubidium, caesum, ammonium, thallium or
even organic radicals ; the second R may be aluminium, iron,
manganese or chromium ; the acid may even be selenic, chro-
mic or manganic, instead of sulphuric. We will briefly describe
the most important alums consisting of double sulphates of
aluminium and another metal, remarking, as with aluminium
sulphate, that their preparation may be found at length in any
chemical treatise.
Potash Alum.
Formula K2S04.Al2(S04)3.24H20, containing 10.7 per cent, of
alumina or 5.7 per cent, of aluminium. Dissolves in 25 parts
of water at 0° and in two-sevenths part at 100°. The solution
reacts acid. It forms colorless, transparent octahedrons, insol-
uble in alcohol. On exposure to air they become opaque,
being covered with a white coating, which is said not to be
efflorescence — a loss of water — but to be caused by absorption
of ammonia from the air. The crystals melt in their water of
<;rystallization, but lose it all above 100°. Heated to redness
it swells up strongly, becomes porous and friable, giving the
product called calcined alum; at whiteness it loses a large part
of its sulphuric acid, leaving a residue of potassium sulphate and
alumina. If it is mixed with one-third its weight of carbon and
calcined, the residue inflames spontaneously in the air. If a
mixture of alumina and bisulphate of potassium is fused and
afterwards washed with warm water, a residue is obtained of
anhydrous alum, or K2S04.Al2(S04)3. The mineral Alunite is
a basic potash alum, K2S04.3(A1A-S0,).6H20.
Ammonia Alum.
Formula (NH0,SO4.Al2(SOl)s.24HjO, containing 11.3 per
■cent, of alumina or 6.0 per cent, of aluminium. Dissolves in
PROPERTIES OF ALUMINIUM COMPOUNDS. 1 29
20 parts of water at 0° and in one-fourth part at 100°. When
heated, the crystals swell up strongly, forming a porous mass,
losing at the same time water and sulphurous acid ; if the tem-
perature is high enough there remains a residue of pure alu-
mina. The temperature necessary for complete decomposition
is higher than that required for volatilizing ammonium sulphate
alone.
Soda Alum.
Formula Na2S04.Al2(S04)3.24H20, containing 11. i per cent,
of alumina or 5.9 per cent, of aluminium. Dissolves in an
equal weight of water at ordinary temperatures. The crystals
effloresce and fall to powder in the air. It is insoluble in abso-
lute alcohol. On account of its great solubility in water it
cannot be separated from ferrous sulphate by crystallization, and
therefore it is either contaminated with much iron or else, to
be obtained pure, special expensive methods must be adopted.
These diflSculties cause the manufacture of soda alum to be in-
significant in amount when compared with potash alum.
Aluminium-Metallic Sulphates.
Sulphate of aluminium forms double sulphates with iron,
manganese, magnesium and zinc, but these compounds are not
analogous to the alums. They are extremely soluble in water,
do not crystallize in octahedrons or any isometric forms, and
their composition is different from the alums in the amount of
water of crystallization. It has heen determined that the double
sulphates with manganese and zinc contain 25 equivalents of
water, which would permit their being considered as combina-
tions of sulphate of aluminium, Al2(S04)3.i8H20, with a sul-
phate of the magnesian series containing seven equivalents of
water, as ZnS04.7H20.
Aluminium Selenites.
By adding a solution of selenite of soda to one of sulphaite
of aluminium maintained in excess, an amorphous, voluminous
9
I30 ALUMINIUM.
precipitate forms, having the composition 4Al2O3.9SeO2.3H2O.
This substance decomposes on being heated, leaving alumina.
If varying quantities of selenious acid are added to this first
salt, other salts of the formulas Al2O3.3SeO2.7H2O, 2Al203.9Se02.
12H2O, Al2O3.6SeO2.SH2O, are formed. These are mostly in-
soluble in water and decompose on being heated, like the first.
Aluminium Nitrate.
Formula A1(N03)3.9H20 is obtained on dissolving aluminium
hydrate in nitric acid. If the solution is evaporated keeping it
strongly acid, it deposits on cooling voluminous crystals having
the formula 2Al(N03)3.isH20. This salt is deliquescent, melts
at 73° and gives a colorless liquid which, on cooling, becomes
crystalline. It is soluble in water, nitric acid, and alcohol ; on
evaporating these solutions it is obtained as a sticky mass. It
is easily decomposed by heat; if kept at 100° for a long time
it loses half its weight, leaving as residue a soluble salt of the
formula 2AI2O3.3N2O5.3H2O. Carried to 140°, this residue
loses all its nitric acid, leaving alumina. On this property is
based a separation of alumina from lime or magnesia, since the
nitrates of these latter bases resist the action of heat much
better than aluminium nitrate.
Aluminium Antimonate.
Al203.3Sb205.isH20 can be prepared by double decomposi-
tion from potassium antimonate and a soluble aluminium salt.
It deposits from solution after several days' standing in shin-
ing, microscopic crystals. At 100° it loses sHjO, at 150°, 2^
H2O more, at 200° it retains only 3H2O and becomes incandes-
cent. Al2O3.Sb2O5.9H2O has been also described.
Aluminium Phosphates.
The normal phosphate, AIPO4, is obtained as a white, gelat-
inous precipitate when a neutral aluminium solution is treated
with sodium phosphate. It is soluble in alkalies or mineral
acids, but not in acetic acid. If a solution of this salt in acids is
PROPERTIES OF ALUMINIUM COMPOUNDS. I3I
neutralized with ammonia, a basic phosphate is precipitated hav-
ing the composition 3Al,(OH)3PO,-|-2Al(OH)3. The mineral
Wavellite has this composition, with nine molecules of water.
The mineral Kalait contains AlP04+Al(OH)3+H20, and when
it is colored azure blue by a little copper it forms the Turquois.
Aluminium meta-phosphate has the formula AIP3O9 or AI2O3.-
3P.O,
Aluminium Carbonate.
If to a cold solution of alum a cold solution of sodium carbon-
ate is added drop by drop, stirring constantly until the solution
reacts feebly alkaline, a precipitate is obtained which, after be-
ing washed with cold water containing carbonic acid gas, con-
tains when damp single equivalents of alumina and carbonic
acid, ALjOa.COij. If the precautions indicated are not used, the
precipitate contains a very small proportion of carbonic acid.
Sestini * states that one litre of water saturated with carbonic
acid gas at the ordinary atmospheric pressure will dissolve 10
milligrammes of alumina, the solution becoming turbid on
boiling or agitation. This reaction is probably the key to the
understanding of the geological formation of native alumina
deposits.
When a solution of sodium bi-carbonate is added to one of
sodium aluminate, a double carbonate of the alkali and alumin-
ium is precipitated, which is easily soluble in acids. (Mende-
leefr.)
Aluminium Borate.
Formula 3AI2OS.BO3. Prepared by Ebelman by heating
together alumina, oxide of cadmium, and boric acid. After
three days' heating the platinum capsule containing the mix-
ture was found covered with transparent crystals of the above
composition, hard enough to scratch quartz and having a spe-
cific gravity of 3. Troost obtained the same substance by
heating alumina in the vapor of boron trichloride. Fremy pre-
pared it by heating fluoride of aluminium with boric acid.
* Gazetta Chim., Vol. 20, p. 313.
132 ALUMINIUM.
Ebelman also obtained it by heating a mixture of alumina and
borax to whiteness ; under these conditions crystals of corun-
dum were formed at the same time.
By precipitating a cold solution of alum with sodium borate,
double salts are obtained containing soda, but which leave on
washing with warm water two compounds having the formulae
zAlA-BOs.sH.O and 3Al203.2B03.8H,0. If the washing is
prolonged too far the two salts are completely decomposed,
leaving a residue of pure alumina.
Aluminium Silicates.
These compounds are very plentiful in nature, both hydrous
and anhydrous. The addition of a soluble aluminium salt to a
solution of sodium silicate would doubtless produce a precipi-
tate of aluminium silicate. Many of 'the native silicates have
been formed by the mingling of lime or alkaline water with
cabonated water carrying alumina in solution. In the native
silicates the silica and alumina occur in many proportions ;
the following ratios of alumina to silica have been observed :
2-1, 3-2, i-i, 2-3, 1-2, 1-3, 1-4, 1-8, thus varying from
tri-basic silicates to pent-acid silicates. The pure silicates
of aluminium alone are infusible before the blowpipe ; but
the presence of other elements, especially the alkalies, calcium
or iron, makes them quite easy to melt. Ordinary blast-
furnace slags are silicates of aluminium, calcium and magne-
sium, and vary from bi-acid to sesqui-basic silicates. In some
of these more basic silicates part of the aluminium present may
exert its acid character, and, in fact, the occurrence of crystals
of magnesium aluminate has been noted in crystallized blast-
furnace slag which was basic and rich in magnesium.
CHAPTER VI.
PREPARATION OF ALUMINIUM COMPOUNDS FOR REDUCTION.
We will consider this division under four heads : —
I. Alumina.
II. Aluminium chloride and aluminium-sodium chloride.
III. Aluminium fluoride and aluminium-sodium fluoride.
IV. Aluminium sulphide.
I.
The Preparation of Alumina.
We will treat this subject in three divisions : —
1 . From Aluminium Sulphate or Alums.
2. From Bauxite.
3. From CryoHte.
I. Preparation of Alumina from Alums or Aluminium
Sulphate.
Hydrated alumina can be precipitated from a solution of any
aluminium salt by ammonium hydrate, an excess of which re-
dissolves a portion. Its chemical formula is ordinarily written
AI2O3.3H2O or A^OHg). The aluminium hydrate thus pre-
cipitated is a pure white, very voluminous, almost pasty mass,
very hard to wash. By boiling and washing with boiUng water
it becomes more dense, but always remain very voluminous.
Washing on a filter with a suction apparatus gives the best re-
sults. At a freezing temperature this hydrate changes into a
dense powder which is more easily washed. On drying, it
shrinks very much in volume and forms dense, white pieces,
transparent on the edges. When dried at ordinary tempera-
tures it has the composition AljOg.H^O. On ignition, the
(133)
134 ALUMINIUM.
Other molecule of water is driven off, leaving anhydrous alu-
mina. After gentle ignition it remains highly hygroscopic, and
in a very short time will take up from the air 1 5 per cent, of
water. In this condition it is easily soluble in hydrochloric or
sulphuric acid. On stronger ignition it becomes harder and
soluble only with difficulty in concentrated acid ; after ignition
at a high temperature it is insoluble, and can only be brought
into solution again by powdering finely and fusing with potas-
sium acid-sulphate or alkaline carbonate. At ordinary furnace
temperatures alumina does not melt, but in the oxy- hydrogen
blow-pipe or the electric arc it fuses to a limpid Hquid and ap-
pears crystalline on cooling.
The precipitation in aqueous solution and subsequent ignition
is not economical enough to be practised on a large scale, and
for industrial purposes the aluminium sulphate or alum is ig-
nited directly. About the easiest way to proceed is to take
ammonia alum crystals, put them into a clean iron pan and
heat gently, when the salt melts in its water of crystallization.
When the water has evaporated, a brittle, shining, sticky mass
remains, which on further heating swells up and decomposes
into a dry, white powder. This is let cool, powdered, put into
a crucible and heated to bright redness. All the ammonia and
almost all the sulphuric acid are thus removed. The rest of
the acid can be removed by moistening the mass with a solu-
tion of sodium carbonate, drying and again igniting ; on wash-
ing with water the acid is removed as sodium sulphate. The
residue, however, will contain some caustic soda, which for its
further use in making aluminium chloride is not harmful. Pot-
ash alum can be treated in a similar way, the potassium sul-
phate being washed away after the first ignition. Still more
easily and cheaply can alumina be made by igniting a mixture
of 4 parts aluminium sulphate and i of sodium carbonate. On
washing, sodium sulphate is removed from the alumina.*
Deville used the following method at Javel : Ammonia alum or
* Kerl and Stohman, 4th Ed., p. 739.
PREPARATION OF ALUMINIUM COMPOUNDS. 135
even the impure commercial aluminium sulphate was calcined,
the residue appearing to be pure, white alumina, but it still con-
tained sulphuric acid, potassium sulphate, and a notable pro-
portion of iron. This alumina is very friable, and is passed
through a fine sieve, and put into an iron pot with twice its
weight of solution of caustic soda of 45 degrees. It is then
boiled and evaporated, and the alumina dissolves even though
it has been strongly calcined. The aluminate of soda produced
is taken up in a large quantity of water, and if it does not show
clear immediately, a little sulphuretted hydrogen is passed in,
which hastens the precipitation of the iron. The liquor is let
stand, the clear solution decanted ofT and subjected while still
warm to the action of a stream of carbonic acid gas. This con-
verts the soda into carbonate and precipitates the alumina in a
particularly dense form which collects in a space not one-
twentieth of the volume which would be taken up by gelatinous
alumina. This precipitate is best washed by decantation, but a
large number of washings are necessary to remove all the sodium
carbonate from it ; it is even well, before finishing the washing,
to add a little sal-ammoniac to the wash-water in order to hasten
the removal of the soda. The well-dried alumina is calcined at
a red heat.
Tilghman* decomposes commercial sulphate of alumina,
Al2(S04)3.i8H20, by filling a red-hot fire-clay cylinder with it.
This cylinder is lined inside with a magnesia fettUng, is kept at
a red heat, the sulphate put in in large lumps, and steam is
passed through the retort, carrying with it vapor of sodium
chloride. This last arrangement is effected by passing steam
into a cast-iron retort in which the salt named is kept melted,
and as the steam leaves this retort it carries vapor of the salt
with it. It is preferable, however, to make a paste of the sul-
phate of alumina and the sodium chloride, forming it into small
hollow cylinders, which are well dried, and then the fire-clay
cylinder filled with these. Then, the cylinder being heated to
* Mierzinski.
136 ALUMINIUM.
whiteness, highly superheated steam is passed over it. The
hydrochloric acid gas which is formed is caught in a condensing
apparatus, and there remains a mass of aluminate of soda,
which is moistened with water and treated with a current of
carbon dioxide and steam. By washing the mass, the soda
goes fnto solution and hydrated alumina remains, which is
washed well and is ready for use.
Mr. Webster's process for making pure alumina at a low price
was incorporated as a part of the Aluminium Co. Ld.'s pro-
cesses. The only description we can give of it is dated 1883.
* Three parts of potash alum are mixed with one part of
pitch, placed in a calcining furnace and heated to 200° or 250°.
About 40 per cent, of this water is thus driven off, leaving sul-
phate of potash and aluminium, with some ferric oxide. After
heating about three hours, the pasty mass is taken out, spread
on a stone floor, and when cold broken to pieces. Hydrochloric
acid (20 to 25 per cent.) is poured upon these pieces, placed
in piles, which are turned over from time to time. When the
evolution of sulphuretted hydrogen has stopped, about five per
cent, of charcoal-powder or lampblack, with enough water to
make a thick paste, is added. The mass is thoroughly broken
up and mixed in a mill, and then worked into balls of about a
pound each. These are bored through to facilitate drying, and
heated in a drying chamber at first to 40°, then in a furnace
from 95° to 150°. The balls are then kept for three hours at'
a low red heat in retorts, while a mixture of two parts steam
and one part air is passed through, so that the sulphur and car-
bon are converted into sulphurous oxide and carbonic oxide,
and thus escape. The current of gas carries over some potas-
sium sulphate, ferrous sulphate and alumina, and is therefore
passed through clay condensers.
The residue in the retorts consists of alumina and potassium
sulphate ; it is removed, ground to fine powder in a mill,
♦Austrian Patent, Sept. 28, 1882; English patent. No. 2580, 1881. Dingier, 1883,
vol. 259, p. 86.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 3/
treated with about seven times its weight of water, boiled in a
pan or boiler by means of steam for about one hour, then
allowed to stand till cool. The solution containing the potas-
sium sulphate is run ofifand evaporated to dryness, the alumina
is washed and dried. The potassium sulphate, as a by-product,
is said to pay one-half the cost of the process.
This deposit contains about 84 per cent, of alumina, while
that obtained by the old process of precipitation has only 65
per cent. Thus a large saving is effected in cost, and 19 per
cent, more alumina is obtained. In addition to this, the whole
of the by-products are recovered, consisting of potassium sul-
phate, sulphur (which is used in making sulphuric acid), and
aluminate of iron.
2. Preparation of Alumina from Bauxite.
At Salindres, the alumina used in the Deville process was
obtained from bauxite by the following processes, which are
in general use for extracting pure alumina from this mineral.
Bauxite is plentiful enough in the south of France, principally
in the departments of Herault, Bouches-du-Rhone, and Var.
It contains as much as seventy-five per cent, alumina. To
separate the alumina from ferric oxide, it is treated with car-
bonate of soda, under the influence of a sufiSciently high tem-
perature, the alumina displacing the carbonic acid and forming
an aluminate of soda, Al^Og.sNa^O, while the ferric oxide re-
mains unattacked. A simple washing with water then permits
the separation of the former from the insoluble ferric oxide.
The bauxite is first finely pulverized by means of a vertical
mill-stone, then intimately mixed with some sodium carbonate.
The mixture is made, for one operation, of —
480 kilos, bauxite.
300 " sodium carbonate of 90 alkali degrees.
This mixture is introduced into a reverberatory furnace, re-
sembling in form a soda furnace, and which will bear heating
138 ALUMINIUM.
Strongly. The mass is stirred from time to time, and it is kept
heated until all the carbonate has been attacked, which is
recognized by a test being taken which does not effervesce
with acids. The operation lasts from five to six hours.
The aluminate thus obtained is separated from ferric oxide by
a washing with warm water. This washing is made at first with
a feeble solution which has served for the complete exhaustion
of the preceding charge, which was last washed with pure
water, forming thus this feeble solution. This gives, on the
first leaching, solutions of aluminate concentrated enough to be
called strong liquor, which are next treated by the current of
carbonic acid gas to precipitate the hydrated alumina. The
charge is next washed with pure water, which completely re-
moves the aluminate ; this solution is the weak liquor, which is
put aside in a special tank, and used as the first leaching liquor
on the next charge treated. This treatment takes place in the
following apparatus (see Fig. i ) : ^ is a sheet-iron vessel, in
the middle of which is a metallic grating, F, on which is held
all round its edges, by pins, a cloth, serving as a filter. A
ought to be closed by a metallic lid held on firmly by bolts.
To work the apparatus, about 500 kilos of the charge to be
washed is placed on the filter cloth, the lid is closed, then
the steam-cock / of the reservoir A is opened. In A is the
weak solution from the last washing of the preceding charge.
The pressure of the steam makes it rise by the tube T into the
filter; another jet of steam, admitted by the cock b, rapidly
warms the feeble liquor as it soaks into the charge. After fil-
tering through, the strong liquor is drawn off by turning the
stop-cock G. The weak solution of the reservoir A is put into
the filter in successive portions, and not all at once ; and after
each addition of solution has filtered through, its strength in
B.° is taken, before any more solution is run in ; then, when the
solution marks 3° to 4°, it is placed in a special tank for weak
liquor, with all that comes through afterwards. Just about this
time, the weak liquor of the reservoir A is generally all used up,
and is replaced by pure water introduced by the tube d. All
PREPARATION OF ALUMINIUM COMPOUNDS.
139
the solutions which filtered through marking over 3° to 4° B.,
are put together, and form a strong liquor which marks about
12° B. This extraction of the aluminate being completed by
the pure water, the residue on the filter is taken out, and a new
operation may be commenced.
Fig. I.
B
bjc
u
-
Li— p
•<
V
G
r^
:
T
1
W
A
-iT
^
i-cvrrrpe O
The strong liquor is introduced into a vessel having an agi-
tator, where a strong current of carbonic acid gas may precipi-
tate the alumina from it. The gas is produced by small streams
of hydrochloric acid continuously falling on some limestone
contained in a series of earthenware jars. The precipitation
vessel is called a baratte. The carbonic acid after having
passed through a washing-flask, is directed to a battery of three
barattes, where the precipitation is worked methodically, so as
to precipitate completely the alumina of each baratte, and util-
I40
ALUMINIUM.
ize at the same time all the carbon dioxide produced. In order
to do this, the gas always enters first into a baratte in which
the precipitation is nearest completion, and arrives at last to
that in which the solution is freshest. When the gas is not all
absorbed in the last baratte, the first is emptied, for the precip-
itation in it is then completed, and it is made the last of the
series, the current being now directed first into the baratte
which was previously second, while the newly charged one is
made the last of the series. The process is thus kept on con-
tinuously. The apparatus used is shown in Fig. 2,
Fig. 2.
u. Charging pipe. b. Steam pipe. i. Steam drip. d. COj enters. / Discharge
pipe. A. Agitator, made of iron rods. C. Tank in which the precipitate settles.
B. Baratte body. D. Steam jacket.
Each baratte holds about 1200 litres of solution, and the
complete precipitation of all the alumina in it takes five to six
hours. A mechanical agitator stirs the contents continually,
and a current of steam is let into the double bottom so as to
PREPARATION OF ALUMINIUM COMPOUNDS. 141
keep the temperature of the solution about 70°. The precipi-
tated alumina and the solution of sodium carbonate which re-
main are received in a vat placed beneath each baratte. The
solution is decanted off clear, after standing, and then evapor-
ated down to dryness, regenerating the sodium carbonate used
in treating the bauxite to make the aluminate, less the inevit-
able losses inseparable from all industrial operations. The de-
posit of alumina contains considerable sodium carbonate me-
chanically intermixed, and is put into a conical strainer to
drain, or else into a centrifugal drying machine, which rapidly
drives out of the hydrated alumina most of the solution of
sodium carbonate which impregnates it ; a washing with pure
water in the drier itself terminates the preparation of the
alumina. At the works at Salindres, a part of this alumina is
converted into sulphate of alumina, which is sold, the remainder
being used for the aluminium manufacture. After washing in
the drier, the alumina presents this composition : —
Alumina 47.5
Water 50.0
Sodium carbonate 2.5
Behnke* produces alumina by igniting bauxite or a similar
mineral with sodium sulphate, carbon, and ferric oxide, using
for each equivalent of alumina present at least one equivalent
of alkali and one-half an equivalent of ferric oxide. The mix-
ture is heated in a muffle or reverberatory furnace. The fritted
product is ground, exposed to the air, and washed with water.
Sodium aluminate goes into solution along with some sodium
sulphate, while ferrous sulphide and undecomposed material
remains as a residue. By passing carbonic acid gas or gases
from combustion through the solution, the alumina is precip-
itated. The residue spoken of is roasted, the sulphurous oxide
given off utilized, and the residue used over in place of fresh
ferric oxide.
R. Lieber f proposes to treat bauxite, aluminous iron ore,
* German Patent (D. R. P.), No. 7256.
t German Patent (D. R. P.), No. 5670.
142 ALUMINIUM.
etc., in a somewhat similar way. These materials are to be
ground fine, mixed with sodium chloride and magnesium sul-
phate (Kieserite), moistened with water, and pressed into
bricks or balls. These are dried and put into a retort heated
red-hot by generator gas. Hydrochloric acid gas is first given
off, sodium sulphate and magnesium chloride being formed.
In a further stage of the process sulphurous oxide is evolved,
the alumina reacting on the sodium sulphate to form sodium
aluminate. The latter is washed out of the residue, and its
alumina precipitated by the ordinary methods.
H. Muller* proposes to extract the alumina from silicates
containing it by mixing them with limestone, dolomite, or
magnesite, also with alkali caustic, carbonate, or sulphate (in
the last case also with carbon), and heating the mixture to
bright-redness. Alkaline aluminate is washed out of the re-
sulting mass, while the residue, consisting of lime, magnesia,
iron oxide, etc., is mixed wifh water-glass and moulded into
artificial stone.
Common salt is said not to react on bauxite if fused with it
alone, but will decompose it if steam is used. Tilghmanf first
used this reaction in 1847. It is said that it was also used at
Nanterre and Salindres previously to 1865. A mixture of
sodium chloride and bauxite was treated in a closed retort and
steam passed through, or, better, in a reverberatory furnace an(J
steam passed over it, at a high temperature. Much sodium
chloride must have been lost by the latter arrangement. The
fused mass was treated with water, when sodium aluminate dis-
solved out.
R. WagnerJ proposed to make a solution of sodium sulphide,
by reducing sodium sulphate by carbon bisulphide, and to boil
the bauxite in it. The sulphuretted hydrogen evolved was to
be absorbed by ferric hydrate; while the sodium aluminate
* German Patent (D. R. P.), No. 12,947.
t Polytechnisches Journal, 106, p. 196.
J Wagner's Jahresb., 1865, p. 332.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 43
was converted into soda and alumina by any of the ordinary
methods.
Laur, a manufacturer of alumina in the south of France, has
attempted to use sodium sulphate instead of the carbonate, in
calcining bauxite. He finds it disadvantageous to exclude the
carbonate altogether, but uses for a bauxite containing 20 per
cent, of ferric oxide and 60 per cent, of alumina, about 66 of
sodium sulphate and 16 of sodium carbonate per 100 of baux-
ite. Carbon must also be mixed with the charge. Under
these conditions the ferric oxide present is first reduced to iron,
which finally becomes iron sulphide. The soda from both the
carbonate and the sulphate combines with the alumina to form
aluminate. An excess of soda is necessary to keep -the
aluminate in solution, and to keep the sulphide of iron out of
solution. The rest of the process is similar to that already de-
scribdti at Salindres.
According to Lowig's experiments, solution of sodium alumi-
nate can be precipitated by calcium, barium, strontium, or
magnesium hydrates, forming caustic soda and hydrated
alumina, the latter being precipitated, together with lime,
baryta, strontia, or magnesia. The precipitate is washed by
decantation, and then divided into two portions, one of which
is dissolved in hydrochloric acid, the other made into a mush
with water, and gradually added to the solution of the first half
until the filtrate shows only a very little alumina in solution.
Chloride of calcium, barium, strontium, or magnesium has been
formed, and the alumina all precipitated.
Dr. K. J. Bayer has made an improvement in the process of
extracting alumina from bauxite, which has received great
commendation from those directly interested in the business,
and who may be supposed to have proved its merits. Dr.
Bayer thus describes it : * Bauxite is fused with sodium car-
bonate or sulphate, and the solution obtained by washing,
containing sodium aluminate, is not decomposed by carbonic
* Stahl und Eisen, Feb. 1889, p. 112.
144 ALUMINIUM.
acid, as formerly, but by the addition of aluminium hydrate
with constant stirring. The decomposition of the solution goes
on until the quantity of alumina remaining in solution is to the
sodium protoxide as i to 6. This preciptation takes place in
the cold, and the pulverulent aluminium hydrate separted out
is easily soluble in acids. The alkaline solution remaining is
concentrated by evaporation, taken up by ground bauxite,
dried, calcined, and melted, and thus goes through the process
again. The use of this caustic soda solution containing alumina
is thus much more profitable than using soda, because by using
the latter only 75 per cent, of the bauxite used is utilized,
whereas by the former all th« alumina dissolved by the solution
is obtained again.
3. Preparation of Alumina from Cryolite.
By the Dry Way. — The following method was invented by
Julius Thomson ; the description is taken principally from Mier-
zinski's " Fabrikation des Aluminiums :" The cryolite is pulver-
ized, an easy operation, and to every lOO parts, 130 to 150
parts of chalk are added, and a suitable quantity of fluorspar
is also used, which remains in the residue on washing after ig-
nition. More chalk is used than is theoretically necessary, in
order to make the mass less fusible and keep it porous. But,
to avoid using too much chalk merely for this purpose, a cer-
tain quantity of coke may be put into the mixture. It is of the"
first importance that the mixture be very intimate and finely
pulverized. It is of greater importance that the mixture be
subjected to just the proper well-regulated temperature while
being calcined. The cryolite will melt very easily, but this is
to be avoided. On this account, the calcination cannot take
place in an ordinary smelting furnace, because, in spite of stir-
ring, the mass will melt at one place or another, while at an-
other part of the hearth it is not even decomposed, because
the heat at the fire-bridge is so much higher than at the farther
end of the hearth. Thomson constructed a furnace for this
special purpose (see Figs. 3 and 4), in which the flame from
PREPARATION OF ALUMINIUM COMPOUNDS.
1 45
the fire first went under the bed of the furnace, then over the
charge spread out on the bed, and finally into a flue over the
roof of the hearth. The hearth has an area of nearly 9 square
metres, being 4 metres long and 2.5 metres wide. It is charged
Fig. 3.
-V.L
twelve times each day, each time with 500 kilos of mixture,
thus roasting 6000 kilos daily, with a consumption of 800 kilos
of coal. The waste heat of the gases escaping from the furnace
Fig. 4.
<=J:
is utilized for drying the soda solution to its crystallizing point,
and the gases finally pass under an iron plate on which the
chalk is dried. In this furnace the mass is ignited thoroughly
without a bit of it melting, so that the residue can be fully
washed with water.
10
146 ALUMINIUM.
The decomposition takes place according to the formula —
2 (AlFs-sNaF) + 6CaC03=Al203.3Na20 + 6CaF, + 6C0„
the resultant product containing aluminate of soda, soluble in
water, and insoluble calcium flouride. The reaction com-
mences at a gentle heat, but is not completed until a red heat
is reached. Here is the critical point of the whole process,
since a very little raising of the temperature above a red heat
causes it to melt. However, it must not be understood that the
forming of lumps is altogether to be avoided. These lumps
would be very hard and unworkable when cold, but they can be
broken up easily while hot, so that they may be drawn out of
the furnace a few minutes before the rest of the charge is re-
moved, and broken up while still hot without any trouble.
The whole charge, on being taken out, is cooled and sieved, the
hard lumps which will not pass the sieve are ground in a mill
and again feebly ignited, when they will become porous and
may be easily ground up. However, the formation of these
lumps can be avoided by industrious stirring of the charge in
the furnace. A well-calcined mixture is porous, without dust
and without lumps which are too hard to be crushed between
the fingers. We would here remark that mechanical furnaces
of similar construction to those used in the manufacture of soda,
potash, sulphate of soda, etc., are more reliable and give the
best results if used for this calcination. The mixture, or ashes,
as the workmen call it, is drawn still hot, and washed while
warm in conical wooden boxes with double bottoms, or the box
may have but one bottom, with an iron plate about "]& milli-
metres above it. A series of such boxes, or a large apparatus
having several compartments, may be so arranged that the
washing is done methodically, i. e., the fresh water comes first
in contact with a residue which is already washed nearly clean,
and the fresh charge is washed by the strong liquor. This is
known as the " Lessiveur methodique," and an apparatus con-
structed especially for this purpose is described in Dingier 186,
376, by P. J. Havrez, but the subject is too general and the de-
PREPARATION OF ALUMINIUM COMPOUNDS. 1 4/
scription too long to be given here. A very suitable washing
apparatus is also the Buff-Dunlop, used in the soda industry
for washing crude soda, and described in Lunge's " Sulphuric
Acid and Alkali," Book II., p. 465. Since the ashes are
taken warm from the furnace the washing water need not be
previously heated, but the final wash-water must be warmed, as
the ashes have been cooled down by the previous washings.
As soon as the strong liquor does not possess a certain
strength, say 20° B., it is run over a fresh charge and so
brought up. The solution contains sodium aluminate.
The carbon dioxide necessary for precipitating the hydrated
alumina may be made in different ways. The gases coming
from the furnace in calcining the cryolite might be used if they
were not contaminated with dust; and there is also the diffi-
culty that exhausting the gases from the furnace would inter-
fere with the calcination. It has also been recommended to
use the gases from the fires under the evaporating pans, by
exhausting the air from the flues and purifying it by washing
with water. This can only be done where the pans are fired
with wood or gas. However, the lime-kiln is almost exclu-
sively used to furnish this gas. The kiln used is shaped like a
small blast furnace. Leading in at the boshes are two flues
from five fire-places built in the brickwork of the furnace, and
the heat from these calcines the limestone. The gases are
taken ofT by a cast-iron down-take at the top. At the bottom
of the furnace, corresponding with the tap hole in a blast fur-
nace, is an opening, kept closed, from which lime is withdrawn
at intervals. A strong blast is blown just above the entrance
of the side flues, and by keeping up a pressure in the furnace,
leakings into it may be avoided. The gas is sucked away from
the top by a pump, which forces it through a cleaning appar-
atus constructed like a wash-bottle, and it is then stored in a
gasometer. Instead of the pump, a steam aspirator may be
used, which is always cheaper and takes up less room.
The precipitation with carbonic acid gas is made by simply
forcing it through a tube into the liquid. The apparatus used
148 ALUMINIUM.
at Salindres is one of the most improved forms. (See p. 140.)
The precipitate is granular, and settles easily. However, it is
not pure hydrated alumina, but a compound of alumina, soda,
carbonic acid, and water, containing usually about —
Alumina ■ 45 per cent.
Sodium carbonate 20 "
Water 35 "
The sodium carbonate must be separated by long-continued
boiling with water, but by this treatment the alumina becomes
gelatinous and diflficult of further treatment. The precipitate
was formerly separated on linen filters, but centrifugal ma-
chines are now preferred. The evaporated solution gives a
high grade of carbonate of soda free from iron. The heavy
residue which is left after the ashes have been lixiviated con-
sists of calcium fluoride with small quantities of ferric oxide,
lime, undecomposed cryolite, and aluminate of soda, and has
not been utilized for any purpose.
R. Biederman* states that if steam is passed over molten
cryolite at a white heat, hydrofluoric acid gas and sodium
fluoride are formed and driven over, while a white, pure crys-
talline mass of alumina remains.
Utilization of aluminous fluoride slags. — At Nanterre, De-
ville used the following process for utilizing in one operation
the slags from the aluminium manufacture and the residues
from the sodium manufacture.
" The slags from making aluminium contain 60 per cent, of
sodium chloride and 40 per cent, of insoluble matter; the
former can be removed by a single washing. The insoluble
material is almost entirely aluminium fluoride, with a little
alumina and undecomposed cryolite. When fluorspar is used
as a flux, the sodium chloride in the slag is in part replaced by
calcium chloride ; but, in general, all the fluorine in the slag is
found combined with the aluminium, which shows the great
affinity between these two elements. The residues left in the
* Karl and Stohman, 4th Ed., p. 819.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 49
sodium retorts deteriorate quickly when exposed to the air, and
contain ordinarily, according to my analysis-^
Carbon 20.0
Carbonate of soda 14.5
Caustic soda 8,3
Sulphate of soda 2.4
Carbonates of lime and iron 29.8
Water 25.0
lOO.O
" To utilize these two materials, 5 to 6 parts of the sodium
residues are mixed carefully with one part of the washed slag,
and the whole calcined at a red heat. The fusion becomes
pasty ; it is cooled and washed, when aluminate of soda goes
into solution, and on treatment with carbon dioxide gives
sodium carbonate and alumina. According to my laboratory
experiments —
1000 grammes of sodium residues
160 " " washed slags
have given
no grammes of calcined alumina
225 " " dry sodium carbonate.
" The residue left on washing the fusion weighs about one-
half the weight of the soda residues used, and contains —
Carbon 30.0
Calcium fluoride 32.0
Alumina 0.6
Various other materials 37.4
" The latter item is formed of ferric oxide, oxide of man-
ganese, a little silica and some oxysulphide of calcium."
Decomposition of Cryolite in the Wet Way. — Deville used the
following method at Javel, which he thus describes; —
" In the Greenland cryolite there are to be found numerous
pieces containing siderite (ferrous carbonate). It is necessary
1 50 ALUMINIUM.
to extract all these pieces before using the mineral as a flux in
producing aluminium. The rejected fragments are then util-
ized by pulverizing them finely, mixing with about three-fourths
of their weight of pure, burnt lime and the whole carefully
slaked. After the slaking, water is added in large quantity,
and the material is heated in a large cast-iron vessel by means
of a steam-coil. A reaction takes place at once, and is com-
plete if the process is well conducted. Some insoluble alum-
inate of lime may be formed, but it can be recovered from the
residue by digesting itwith some solution of carbonate of soda.
The residue remaining is calcium fluoride, which settles easily,
and the clear liquor decanted off contains aluminate of soda,
from which alumina can be precipitated as before. The cal-
cined alumina obtained may contain iron when the cryolite
used contains a large amount of ferrous carbonate. It has ap-
peared to me that the latter mineral may be decomposed by
the lime, and some protoxide of iron be thus dissolved by the
soda in small quantity."
"We make alumina by this method at Nanterre only because
it utilizes the impure pieces of cryolite and works in conveni-
ently with the previously-described processes for utilizing the
slags."
An ingenious modification of the above process was devised
by Sauerwein. The first reaction is the same, five parts of
finely-powdered cryolite being boiled with four parts of burnt
lime, as free as possible from iron, producing a solution of
sodium aluminate and a residue of insoluble calcium fluoride.
Tissier recommended using two parts' of cryolite to one of lime,
but with these proportions only about one-third of the alumin-
ium in the cryolite is converted into soluble aluminate. Hahn
claims that complete decomposition takes place by using xoo
parts of cryolite to 88 parts of burnt lime. The solution is set-
tled, washed by decantation, and these washings put with the
strong solution first poured off; the next washings are reserved
for the fresh wash-water of another operation. The solution of
sodium aluminate is then boiled with a quantity of cryolite
PREPARATION OF ALUMINIUM COMPOUNDS. 151
equal to the amount first used, when sodium fluoride is formed
and alumina precipitated. This operation is in no way diffi-
cult, only requiring a little more attention than the first.
The alumina thus made is very finely divided. The reactions
involved are :
2(AlF3.3NaF) + 6CaO = AlA-sNa^O + 6CaF,.
2(AlFF3.3NaF) + AlA-sNa^O + 6H,0 = aCAlA-sH^O) + izNaF.
During the last operation it is best to add an excess of cryo-
lite, and keep the liquid in motion to prevent that mineral from
caking at the bottom. Lead is the best material to make these
precipitating tanks of, since iron would contaminate the alumina.
The precipitate is washed as in the previous operation. The
solution of sodium fluoride is boiled with the requisite quantity
of burnt lime, which converts it into caustic soda, NaOH, which
is separated from the precipitated calcium fluoride by decanta-
tion and washing.
In the establishment of Weber, at Copenhagen, where at one
time all the cryolite produced in Greenland was received, the
mineral was decomposed by acid. Hydrochloric acid attacks
the mineral slowly, but sulphuric acid immediately dissolves
the sodium fluoride, with disengagement of hydrofluoric acid ;
gelatinous aluminium fluoride separates out, and is attacked
more slowly. The cryolite requires nearly i ^ parts of sul-
phuric acid to dissolve it, the reaction being :
2(AlF3.3NaF) + 6H2SO4 = AlsCSO^s + 3Na,S04+ 12HF.
The solution is evaporated and crystallized, when the sodium
sulphate crystallizes out, and the mother liquid is treated for its
alumina. This method is too costly, when compared with more
recent processes, to be used at present.
According to Schuch* very finely-powdered cryoHte is dis-
solved by a large excess of hot dilute soda solution, but is
thrown down unaltered when carbonic acid gas is passed through
* Polytechnisches Journal, 165, p. 443.
152 ALUMINIUM.
the solution. An excess of concentrated soda liquor converts
the mineral into sodium aluminate and sodium fluoride, the for-
mer being soluble but the latter almost insoluble in the soda
solution.
II.
The Preparation of Aluminium Chloride and
Aluminium-Sodium Chloride.
Anhydrous aluminium chloride cannot be made by evap-
orating the solution of alumina in hydrochloric acid, for, as we
have seen, decomposition of the salt sets in, hydrochloric acid
is evolved and alumina remains. The same phenomena occur
on evaporating a solution of the double chloride. These anhy-
drous chlorides are prepared by a method discovered by
Oerstedt, applicable to producing a number of similar metallic
chlorides, which consists in passing a current of dry chlorine
gas over an ignited mixture of alumina and carbon.
Wohler* proceeded as follows in preparing the aluminium
chloride which was used in his early experiments : " Alumina is
mixed with charcoal powder and made plastic with oil. Cylin-
ders of about 5 millimetres diameter are made of this paste,
placed in a crucible with charcoal powder and heated until no
more combustible gases distil. After cooling the crucible the
cylinders are taken out, and a porcelain or glass tube open at
both ends filled with them. This is then placed in a combus-
tion furnace, connected at one end with a chlorine generator,
and at the other with a tubular extension from the further end
of which the gases escape, either into the air or into a flask
filled with milk of lime. When the whole apparatus is ready,
and filled with well-dried chlorine gas, the tube is heated to
glowing, when aluminium chloride is formed and condenses in
the extension of the tube."
Deville paid great attention' to the production and purifica-
*Pogg. Ann., n, p. 146.
PREPARATION OF ALUMINIUM COMPOUNDS.
153
tion of aluminium chloride ; the following is his account of the
processes used at Javel :
Manufacture on a Small Scale. — " I took 5 kilos of alumina
and mixed it with 2 kilos of carbon and a little oil ; the paste
was made into balls and ignited at a bright-red heat. The
compact, coke-like mass resulting was broken in pieces and
put, with its powder, into a stoneware retort, C (Fig. 5),
having a capacity of about 10 litres, and terminating in a neck.
Fig. s.
D. This retort was put in a furnace and heated to redness,
while a current of dry chlorine gas passed in by the tube A.
During the first few moments considerable quantities of water
vapor escape from the neck. When aluminium chloride distils,
as is shown by dense, white fumes, a porcelain or stoneware
funnel, E, is adjusted to the neck D, and kept in place by fill-
ing the joint with fine asbestos and then luting it over with a
little potter's clay mixed with hair. Against this funnel fits a
globular vessel, F, the joint being made tight in a similar way.
This apparatus condenses and holds all the chloride distilled.
However fast the chlorine may pass into the retort, it is so well
absorbed during three-fourths of the operation that not a trace
is mixed with the carbonic oxide escaping. However, the gas
always fumes a little, because of a small quantity of silicon
chloride being formed by the chlorine and carbon attacking the
sides of the retort, or from chloride of sulphur or a little chlor-
154 ALUMINIUM.
oxycarbonic acid. When the globe F is filled it is taken away
to extract the coherent, crystalline aluminium chloride it con-
tains, and is replaced immediately by another. During one
operation three jars were thus filled, and altogether a little over
lO kilos of chloride obtained. In the retort there remained
almost a kilo of coke mixed with alumina in the proportion of
two of carbon to one of alumina, making 330 grammes of the
latter remaining unattacked out of S kilos. This coke contains
also some double chloride of alumina and potassium and a little
calcium chloride, which render it deliquescent. This residue
was washed, mixed with a fresh quantity of alumina, and em-
ployed in a new operation."
Manufacture on a large scale. — " In applying this process on
a large scale, the oil and carbon were replaced by tar, the
alembic by a gas-retort, and the glass receiver by a small brick
chamber lined with glazed tiles. The alumina was obtained by
calcining ammonia alum in iron pots ; the residue obtained by
one calcination at a bright-red heat was mixed with pitch, to
which a little charcoal dust was added. The paste was well
mixed, introduced into iron pots, covered carefully and heated
until all vapors of tar ceased burning. The aluminous carbon
is used while it is still hot, if possible, as it is quite hygroscopic.
(This aluminous carbon conducts electricity wonderfully well ;
it is the best electrode to use in making aluminium by the bat-
tery, since its alumina regenerates the bath.) The residue is
hard, porous, and cracked, and contains sulphur from the sul-
phuric acid of the alum, a little iron, phosphoric acid in small
quantity, a perceptible proportion of lime, and finally potash,
which is always present in alums made from clay. The chlo-
rine gas used was conducted by lead pipes and passed over
calcium chloride before being used. The retort used was of
about 300 litres capacity, and was placed vertically in a sort of
chimney, C (Fig. 6), the flame circulating all around it. In
the bottom was a square opening, x, about 20 centimetres
square, which could be closed by a tile kept in place by a screw,
V. A porcelain tube pierced the sides of the furnace and en-
PREPARATION OF ALUMINIUM COMPOUNDS.
ISS
tered the retort at O; it was protected from the flame by a fire-
clay cyHnder inclosing it. At the top, the retort was closed by
a tile, Z, of refractory brick, in the centre of which was made
a square opening, W, oi \o \.o \2 centimetres side. Finally, an
opening, X, placed 30 centimetres below the plate Z, gave
issue to the vapors distilled, conducting them into the chamber
L. This condensation chamber was about i metre cube ; it had
Fig. 6.
one wall of bricks in common with the furnace, thus keeping
it rather hot. The other walls should be thin and set with
close joints and very little mortar. The cover, M, was mov-
able ; it and the sides of the chamber were of glazed tiles. An
opening 20-30 centimetres square in the lower part of the
chamber communicated with flues lined with lead, for a little
chloride was drawn into them. The uncondensed gas passed
to a chimney.
" To work such an apparatus it is necessary, first of all, to
dry it with the greatest care in all its parts, especially the con-
densation chamber. The retort is slowly heated and is left
156 ALUMINIUM.
Open at Z until it is judged quite dry, and is then filled with
red-hot, freshly-calcined mixture of carbon and alumina. The
top cover is then replaced, and the fire urged until the retort is
at a dark-red heat all over. Finally, chlorine is passed in, but
the opening at W is kept open ; the gas is allowed to pass into
the condensation chamber only when fumes of aluminium
chloride appear very abundantly at W. When the operation
proceeds right, almost all the aluminium chloride is found at-
tached in a dense, solid mass to the cover M. I have taken
out at one time a plate weighing almost 50 kilogrammes, which
was less than 10 centimetres thick; it was made up of a large
number of sulphur-yellow crystals penetrating each other and
looking like stalactites and long soda crystals. When it is
judged that the material in the retort is almost exhausted, the
hole X is opened, the residue scraped out, and fresh mixture
put in. During the operation there should be no white vapors
coming from the condensation chamber, but the odor of gas
will always be sharp because of the silicon chloride present,
formed unavoidably by the chlorine attacking the retort. A
gas retort, handled well, should last continuously two or three
months, or even more. The furnace should be constructed so
as to permit its easy replacement without much expense.
When in use, the retort is closely watched through spy-holes in
the wall, and any cracks which may appear promptly plastered
up, if not large, with a mixture of fine asbestos and soda
glass."
Purification of aluminium chloride. — " It often happens that
the chloride obtained is not pure, either from the nature of the
apparatus employed, or from neglect of the many precautions
which should be taken. In this case, to purify it, it is heated
in an earthen or cast-iron vessel with fine iron turnings. When
the hydrochloric acid, hydrogen and permanent gases are
driven from the apparatus, it is closed and heated hotter, which
produces a light pressure under which influence the aluminium
chloride melts and enters into direct contact with the iron.
The ferric chloride, which is as volatile as aluminium chloride.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 57
is transformed into ferrous chloride, which is much less volatile,
and the aluminium chloride can be obtained pure by being
volatilized away or distilled in an atmosphere of hydrogen."
When the processes just described were put in use at the
chemical works at La Glaciere, great care had to be taken to
avoid letting vapors and acid gases escape into the air, since
the works were surrounded by dwellings. To avoid these in-
conveniences, the vapor of aluminium chloride was made to
enter a heated space in which was sodium chloride, in order to
produce the less volatile double chloride; but the apparatus
choked up so persistently that the attempt was given up. It
then occurred to Deville to put sodium chloride into the mix-
ture itself in the retort. The same apparatus was used as be-
fore, except that the large gas-retort had to be replaced by a
smaller earthen one, which could be heated much hotter, the
grate being carried half way up the retort.* The condensation
chamber had to be replaced by a small earthen vessel. The
double chloride produced is fusible at about 200°, and is quite
colorless when pure, but colored yellow by iron. It is, more-
over, very little altered in dry air when in compact masses, and
can be easily handled. When the double chloride is obtained
quite pure, it gives up its aluminium completely when reduced
by sodium.
The following description by M. Margottetf will show the
form of apparatus used in 1882 by the French company carry-
ing on the Deville process at Salindres : —
The double chloride may be obtained in the same manner as
the simple chloride ; it is sufficient to put some common salt,
NaCl, into a mixture of alumina and carbon, and on heating
this mixture strongly there is formed, by the action of the
chlorine, aluminium-sodium chloride, which distils at a red heat
and condenses in a crystalline mass at about 200°. The hy-
* It was when first using this process that Deville borrowed some zinc retorts from
the Vielle Montagne works, and since they contained a little zinc in their composition
the aluminium made for a while was quite zinciferous.
t Fremy's Ency. Chimique.
158
ALUMINIUM.
drated alumina obtained in the preceding operation is mixed
witli salt and finely pulverized charcoal, in proper proportions,
the whole is sifted, and a mixture produced as homogeneous
as possible ; then it is agglomerated with water and made into
balls the size of the fist. These balls are first dried in a drying
stove, at about 150°, then calcined at redness in retorts, where
the double chloride should commence to be produced just as
the balls are completely dried. These retorts are vertical cyl-
inders of refractory earth ; each one is furnished with a tube in
its lower part for the introduction of chlorine, and with another
towards its upper end for the exit of the vapor of double chlo-
ride (see Fig. 7). A lid carefully luted during the operation
Fig. 7.
with a mixture of fine clay and horse-dung serves for the charg-
ing and discharging of the retort. The double chloride is con-
densed in earthen pots like flower-pots, made of ordinary clay,
and closed by a well-luted cover, into which passes a pipe of
clay to conduct the gas resulting from the operation into flues
connected with the main chimney. Each retort is heated by a
fire, the flame of which circulates all round it, and permits
keeping it at a bright red heat. An operation is conducted as
follows : The retort is filled with stove-dried balls, the lid is
PREPARATION OF ALUMINIUM COMPOUNDS. 1 59
carefully luted, and the retort is heated gently till all the mois-
ture is driven off. This complete desiccation is of great im-
portance, and requires much time. Then chlorine, furnished
by a battery of three generating vessels, is passed in. During
the first hours, the gas is totally absorbed by the balls ; the
double chloride distils regularly for about three hours, and runs
into the earthen pots, where it solidifies. Toward the end, the
distillation is more difficult and less regular, and the chlorine is
then only incompletely absorbed. After each operation there
remains a little residue in the retort, which accumulates and is
removed every two days, when two operations are made per
day. One operation lasts at least twelve hours, and a retort
lasts sometimes a month. The double chloride is kept in the
pots in which it was condensed until the time it is to be used
in the next operation ; it is almost chemically pure, save traces
of iron, and is easy to keep and handle.
The following estimate was made by Wurtz, in 1872, show-
ing the cost of a kilo of aluminium-sodium chloride as made
by the above process: —
Anhydrous alumina 0.59 kilos @ 86 fr. per 100 kilos = o it. 50.7 cent.
Manganese dioxide 3.74 " " 14 " " " " = o " 52.3 "
Hydrochloric acid 15.72 " " 3" " " " =0" 47.1 "
Coal 25.78 " " 1.40 ' =0" 36.1 "
Wages o" 23.8 "
Expenses o " 38.0 "
Total 2 fr. 48.0 cent.
This is equal to about 22^ cents per pound. An average
of 10 kilos of this was used to produce one kilo of aluminium,
which shows a yield of only 70 per cent, of the contained alu-
minium, and an increased cost of 6y cents on every pound of
aluminium from the imperfection of reduction. In this respect
there certainly seems large room for improvement.
The largest plant ever erected for the manufacture of alu-
minium-sodium chloride was that of the Aluminium Co. Ltd.,
at Oldbury, near Birmingham, England. The plant was com-
menced in the latter part of 1887, and was in working order in
l6o ALUMINIUM.
July, 1888. The process is in principle indentical with that used
at Salindres, but the whole was on such a large scale that the
description is still interesting.
Twelve large regenerative gas furnaces are used, in each of
which are placed five horizontal fire-clay retorts about 10 feet
in length, into which the mixture is placed. These furnaces are
in two rows, of six each, along each side of a building about
250 feet long, leaving a clear passage down the centre 50 feet
wide. Above this central passage is a platform swung from
the roof, which carries the large lead mains to supply chlorine
to the retorts ; opposite each retort is a branch pipe controlled
by a valve. The valves are designed so that the chlorine must
pass through a certain depth of (non-aqueous) liquid, thus
regulating the flow and preventing any back pressure in the re-
tort from forcing vapor into the main. The opposite or back
ends of the retorts are fitted with pipes which convey the vapor
of the double chloride into cast-iron condensers and thence into
brick chests or boxes, the outsides or ends of which are closed
by wooden doors fitting tightly. Convenient openings are ar-
ranged for clearing out the passages, which may become
choked because of the quickness with which the double chlor-
ide condenses. On looking down the centre of the building it
presents the appearance of a double bank of gas retorts for
making ordinary illuminating gas, except that the retorts are
only one-high. (Fig. 8).
The chlorine plant is on a correspondingly large scale, the
usual manganese-dioxide method being employed and the spent
liquor regenerated by Weldon's process. The chlorine gas is
stored in large gasometers from which it is supplied to the re-
torts at a certain pressure. The mixture for treatment is made
by mixing hydrated alumina with common salt and carbon in
the form of charcoal powder or lamp-black. This being well
mixed is moistened with water, thrown into a pug-mill from
which it is forced out as solid cylinders, and cut into about 3
inch lengths by a workman. The lumps are then piled on top
of the large chloride furnaces to dry. In a few hours they are
PREPARATION OF ALUMINIUM COMPOUNDS.
I6I
hard enough to allow handling, and are put into large wagons
and wheeled to the front of the retorts.
When the retorts are at the proper temperature for charging,
the balls are thrown in until the retort is quite full, the fronts
are then put up and luted tightly with clay, and the charge left
alone for about four hours, during which the water of the hy-
drated alumina is completely expelled, the rear end of the re-
tort being disconnected from the condensing chamber, which
Fig. 8.
must be kept perfectly dry, and connected directly with the
chimney. At the end of this time the chlorine is turned on
and the retort connected with the receiver. At first the chlo-
rine passed in is all absorbed by the charge and only carbonic
oxide escapes into the boxes, where it is ignited and burns,
thus warming them up. After a certain time dense fumes are
evolved, and then the condensers are shut tightly and the un-
condensed gases pass into the chimney. The chlorine is passed
in for 72 hours in varying quantity, the boxes at the rear being
opened from time to time by the workmen to note the pro-
gress of the distillation. The greater part of the double chlo-
II
1 62 ALUMINIUM.
ride liquefies and trfckles down to the floor of the chambers,
but a portion sublimes and condenses on the walls as a yellow
crystalline powder. These chambers are emptied from time to
time and the contents packed away in air-tight wooden chests,
that it may keep without absorbing moisture from the air. At
the end of the distillation the chlorine valves are closed and
the condenser boxes cleaned out ; the retorts are also opened
at their front end and the residue raked out. This residue
consists of a small quantity of alumina, charcoal and salt, and
is remixed in certain proportions with fresh material and used
over again. The retorts are then immediately re-charged and
the operations repeated. Each set of five retorts produces
about 1600 to 1800 lbs. in one operation, or say 3500 lbs. per
week. The twelve furnaces are therefore capable of producing
easily 1,500,000 lbs. of double chloride per annum. Since 10
lbs. of this salt are required to produce i lb. of aluminium, the
capacity of the works is thus seen to be 150,000 lbs. or over of
metal per year.
This last remark as to the proportion of chloride required to
form the metal will show the absolute necessity there is to keep
iron from contaminating the salt. This gets in, in varying pro-
portions, from the iron in the materials used and in the fire-clay
composing the retort, and exists as ferrous and ferric chlorides.
Exercising the utmost care as to the purity of the alumina and
charcoal used, and after having the retorts made of a special
fire-clay containing a very small percentage of iron, it was found
impossible to produce a chloride on a large scale containing less
than 0.3 per cent, of iron. This crude chloride is highly de-
liquescent and varies in color from light yellow to dark red —
the color depending not so much on the absolute amount of
iron present as on the proportion of iron present as ferric salt,
which has a high color. Since practically all the iron present
in the salt passes into the aluminium, it is seen that the latter
would contain 3 per cent, or more of iron. For some time the
only way to obviate this difficulty was to resort to purifying the
aluminium, by which the content of iron was finally reduced to
PREPARATION OF ALUMINIUM COMPOUNDS. 1 63
2 per cent. Mr. Castner has since perfected a process for
purifying the double chloride by which only o.oi per cent, of
iron is left in it. The principle employed in doing this is de-
scribed in the patent claims* to be the reduction of the iron salts
to metallic iron by melting the chloride (single or double) with
a quantity of metallic aluminium or sodium sufiScient for this
purpose. The purified chloride is quite white and far less de-
liquescent than the crude salt, which seems to indicate that the
iron chlorides have a large share in rendering the crude salt so
deHquescent. The purified chloride is preserved by melting
and running into tight iron drums. A process of purification
used later by Mr. Castnerf consisted in separating out the iron
electrolytically. The melted salt was passed slowly along a
trough on the sides of which were electrodes kept at a tension
sufficient to decompose the iron chlorides, the tension also
being gradually decreased from one end to the other propor-
tionally to the decreasing quantity of iron in the material as it
passed along.
The success of the manufacture of the double chloride is said
to depend on the proportions of the mixture, the temperature
of the furnace, the quantity of chlorine introduced, and the de-
tails of construction of the retorts ; but very little information
on these points has been made public. The following figures
may give some idea of the quantities of materials used : The
production of 1000 lbs. of double chloride is said to require —
Common salt 357 lbs.
Hydrated alumina 491 "
Chlorine gas 674 "
Coal 1800 "
The salt and hydrated alumina are therefore mixed in about
the same proportion as those indicated by the formula which
represents the reaction
*U. S. Patent, No. 409,668, Aug. 27, 1889.
tU. S. Patent, No. 422,500, March 4, 1890.
1 64 ALUMINIUM.
Al,C3+2NaCl+3C+6Cl=Al,Cl6.2NaCl+3CO.
for if we assume the hydrated alumina used to contain 90 per
cent, of that compound, the 491 lbs. of it used would corres-
pond to very nearly the amount of salt said to be used. As
to the cost of this double chloride, so many uncertain elements
enter into it that it cannot be satisfactorily estimated from the
data at hand. We are informed, however,* that the double
chloride used represented 43 per cent, of the cost of aluminium
to this company. If we place the total cost at 8 shillings per
lb. this would indicate a trifle over 4 pence per lb. as the cost
of the double chloride. It was probably not over 3 pence.
H. A. Gadsden,! of London, patented a method of obtaining
aluminium, in which the aluminium chloride used is obtained by
a method similar in all respects to the process as described by
Deville, except that the corundum or bauxite used is mixed
with about 10 per cent, of sodium or potassium fluoride and a
small quantity of fluorspar. After this has been mixed and
calcined it is pulverized, 10 per cent, of charcoal dust added,
made into balls and heated in a muffle until pasty. Taken
out of the muffle they are then put into a retort, heated highly,
and chlorine gas passed over them, when aluminium chloride
distils.
Count R. de Montgelas| patents a process for producing
aluminium chloride and the double chloride with sodium, in •
which the only difference from the preceding methods is that
molasses is used instead of pitch for moulding the mixture into
balls, the mixture otherwise containing alumina, charcoal, and
sodium chloride ; and it is claimed that by regulating the heat
at which chlorine is passed over this mixture, previously cal-
cined, aluminium chloride can be volatilized while aluminium-
sodium chloride remains in the retort. The use of horizontal
retorts is recommended.
*Zeitschrift des Verein Deutscher Ingenieure, 1889, p. 301.
t German Patent (D. R. P.) No. 27,572 (1884).
I English Patents Nos. 10,011, 10,012, 10,013, Aug. 4, 1886.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 65
Prof. Chas. F. Mabery,* of the Case School of Applied Sci-
ence, Cleveland, patented and assigned to the Cowles Bros, the
process of making aluminium chloride, consisting in passing
dry chlorine or hydrochloric acid gas over an alloy of alumin-
ium and some other metal kept in a closed vessel at a temper-
ature sufficient to volatilize the aluminium chloride formed,
which is caught in a condenser. Or, hydrochloric acid gas is
passed through an electrically heated furnace, in which alumina
is being decomposed by carbon, a condenser being attached to
the opposite end of the furnace.
Mr. Paul Curiej states that aluminium chloride can be made
by passing vapors of carbon disulphide and hydrochloric acid
either simultaneously or successively over ignited alumina or
clay. The first forms aluminium sulphide, which the latter
converts into the volatile chloride, which distils.
H. W. WarrenI recommends the following process as of gen-
eral application in producing anhydrous metallic chlorides.
Petroleum is saturated with either chlorine or hydrochloric acid
gas, both gases being soluble in it to a large extent, particu-
larly the latter gas. This operation is performed at a low tem-
perature, as more of the gases is then dissolved. The oxide of
the metal, alumina, for instance, is put into large earthenware
retorts, and raised to red heat. The saturated oil is then boiled
and its vapor passed into the retort. On contact with the
oxide a strong reaction commences, fumes of aluminium chlor-
ide are at once evolved, and distil into a condenser, the opera-
tion being continued until no more white fumes appear. Then
fresh alumina is supplied, and the reaction continues. The
aluminium chloride may be purified from any oil by gentle ap-
plication of heat. Mr. Warren also used naphthaline chloride
with advantage, as also chloride of carbon, but their high price
rendered them unable to compare with petroleum in economy.
* U. S. Patent, Oct. 26, 1886.
t Chemical News, 1873, p. 307.
J Chemical News, April 29, 1887.
1 66 ALUMINIUM.
Aluminium bromide can be similarly prepared by substituting
bromine for chlorine.
Camille A. Faure, of New York, the well-known inventor of
the Faure storage battery, has patented* a process for produc-
ing aluminium chloride, which is very similar to the above
method. The manipulation is described as follows : An oxy-
genated ore of aluminium is brought to about a red heat by
bringing it, in a furnace, into direct contact with the flame.
When at proper heat the flame is cut off and a gas containing
carbon and chlorine introduced. A mixture of petroleum vapor
or a similar hydrocarbon with hydrochloric acid gas is pre-
ferred. Vaporized chloride of aluminium immediately passes
off into a condenser.
In a paper written by Mr. Faure, and read before the French
Academy of Sciences by M. Berthelot,t it was stated that the
aim of this process was to suppress the prominent disadvant-
ages of the older methods : viz., cost and wear and tear of re-
torts, great consumption of fuel, slowness of the operation,
large amount of labor, and cost of the chlorine. For this pur-
pose the chlorine is replaced by hydrochloric acid gas and the
carbon by a hydrocarbon. Since all pure hydrocarbons are
decomposed at a red heat with deposition of carbon, the pro-
cess would appear impracticable ; but a proper mixture of hy-
drochloric acid gas and naphthaline vapor is said not to de-
compose by the highest temperature alone, a new compound
being formed, a sort of napthaline chloride, which is exceed-
ingly corrosive and powerful enough to attack any oxide and
convert it into chloride. To carry out the process a gas fur-
nace with large bed is used. On this is spread a layer of small
pieces of bauxite about two feet deep. The flame comes in
over the ore, passes downward through it and through numer-
ous holes arranged in the hearth, and thence to a chimney. In
this way the heat of the gases is well utilized, while the layer
* U. S. Patent, No. 385,345, July 3, 1888.
t July 30, 1888.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 67
of bauxite is heated to whiteness on top and to low-red at the
bottom. The flames are then turned off and the mixture of
naphthaHne and hydrochloric acid vapors passed upward
through the bed, and by their reaction producing aluminium
chloride, which is diverted by suitable flues into a condenser.
It is claimed that by careful fractional condensation the chlor-
ides of silicon, iron, calcium, etc., formed from impurities in
the bauxite, can be easily separated, that of silicon being
more volatile and those of iron and calcium less volatile than
aluminium chloride. As naphthaline is a bye-product from
gas-works, it is claimed that it can be bought for i ^ cents per
lb., and that only j^ oi a lb. is used per lb. of aluminium chlo-
ride produced. It is also claimed that one furnace, with two
men to work it, will produce 4000 lbs. of chloride a day. The
estimated cost of the chloride is about i }4 cents per pound, of
which 17 per cent, is for beauxite, 47 per cent, for hydrochloric
acid, 27 per cent, for naphthaline, and 9 per cent, for labor.
Mr. Faure experimented in the vicinity of New York during
1889, and was sanguine of having the process at work in 1890,
but no commercial process has resulted from these efforts.
(See further. Chap. XI.)
In all the processes for producing aluminium chloride so far
considered, the use of common clay was not recommended,
since silicon chloride is formed as well as aluminium chloride.
The only method proposed for using clay for this purpose is
that of M. Dullo, nearly twenty years ago, and which cannot
have been very successful, since it has not been heard of in
operation. We will repeat his remarks, however, for there is
still a large field open in the utilization of clay for the manu-
facture of aluminium, and since the metal is becoming so cheap
the manufacturers are not above looking for and utilizing the
cheapest raw material available.
* " Aluminium chloride may be obtained easily by direct
treatment of clay. For this purpose a good clay, free from iron
and sand, is mixed with enough water to make a thick pulp,
* Bull, de la Soc. Chem., i860, vol. v., p. 472.
1 68 ALUMINIUM.
to which are added sodium chloride and pulverized carbon.
For every lOO parts of dry clay there are taken I20 parts of
salt and 30 of carbon. The mixture is dried and broken up
into small fragments, which are then introduced into a red-hot
retort traversed by a current of chlorine. Carbonic oxide is
disengaged, while at the same time aluminium chloride and a
little silicon chloride are formed. It is not necessary that the
chlorine should be absolutely dry, it may be employed just as
it comes from the generator. The gas is absorbed very rapidly,
because between the aluminium and silicon there are reciprocal
actions under the influence of which the chemical actions are
more prompt and energetic. The aluminium having for chlo-
rine a greater afifinity than silicon has, aluminium chloride is
first formed, and it is only when all the aluminium is thus trans-
formed that any silicon chloride is formed. When the latter
begins to form the operation is stopped, the incandescent mix-
ture is taken out of the retort and treated with water. The
solution is evaporated to dryness to separate out a small quan-
tity of silica which is in it, the residue is taken up with water,
and aluminium-sodium double chloride remains when the
filtered solution is evaporated to dryness."
We must say of M. Dullo's suggestions that it is the general
experience that the more volatile silicon chloride is formed
first; it is also very improbable that a solution of aluminium-
sodium chloride can be evaporated without decomposition.
III.
The Preparation of Aluminium Fluoride and
Aluminium-Sodium Fluoride (Cryolite).
Natural cryolite is too impure for use in many operations
which aim to produce very pure aluminium. Schuh has pro-
posed boiling the mineral in solution of soda. Under certain
conditions sodium aluminate is formed (see p. JJI), but if the
solution of soda is dilute the liquor remains clear after taking
up the cryolite, and on passing a current of carbonic acid gas
PREPARATION OF ALUMINIUM COMPOUNDS. 1 69
through it aluminium-sodium fluoride is precipitated. In this
way the pure double fluoride can be separated from impure
cryolite.
Berzelius recommended preparing artificial cryolite by de-
composing aluminium hydrate by a solution of sodium fluoride
and hydrofluoric acid, the hydrate being added to the liquid
until its acidity was just neutralized : —
A1,03.3H,0 + 6NaF + 6HF = 2(AlF3.3NaF) + 6H,0.
Deville states that on adding sodium chloride to a solution
obtained by dissolving alumina in an excess of hydrofluoric
acid, a precipitate of cryolite is obtained. Since cryolite is
hardly attacked at all by hydrochloric acid, it is probable that
the reaction occurring is
AIF3 + 3HF + sNaCl = AlFa.sNaF + 3HCI.
The process which Deville recommended as best, however, is
the treatment of a mixture of calcined alumina and carbonate
of soda, mixed in the proportions in which their bases exist in
cryolite, by an excess of pure hydrofluoric acid : —
AliiOa -I- sNa/'Os + i2HF=2(AlF.3NaF) -|- 3CO2 + 6H2O.
100 parts of pure alumina requiring 310 parts of sodiurri car-
bonate and 245 of anhydrous hydrofluoric acid, there being
410 parts of cryolite formed. On drying the mass and melting
it there results a limpid, homogeneous bath having all the
characteristics of cryolite, being reduced by sodium or by an
electric current, which would not result from a mere mixture ot
alumina and sodium fluoride melted together.
Deville also states that when anhydrous aluminium chloride
is heated with sodium fluoride in excess, a molten bath results
of great fluidity, and on cooling and dissolving away the excess
of sodium fluoride by repeated washings the residue is similar
to cryolite, while the solutions contain no trace of any soluble
aluminium salt: —
AICI3 + 6NaF=AlF3.3NaF 4- sNaCl.
I/O ALUMINIUM.
It is evident, however, that the above reaction would be the
reverse of a profitable one, and is therefore not of economical
utility.
Pieper* patents a very similar reaction, but operates in the
wet way. A solution of aluminium chloride is decomposed by
adding to it a suitable quantity of sodium fluoride in solution.
Sodium chloride is formed and cryolite precipitated, as in the
last reaction given. By adding different proportions of sodium
fluoride solution, precipitates of double salts are obtained, con-
taining varying proportions of the two fluorides. The use of
aluminium chloride in solution would dispense with the objec-
tion made to Deville's analogous method, and this process
would very probably produce cryolite quite cheaply.
Brunerf produced aluminium fluoride by passing hydro-
fluoric acid gas in the required quantity over alumina heated
red hot in a platinum crucible: —
Al20, + 6HF=2A1F3 4 3H2O.
Devillef states that it can be made by melting together the
equivalent quantities of cryolite and aluminium sulphate :
2(AlF3.3NaF) -I- Al,(S04)3.:eH,0 = 4AIF3 + sNa^SO^ + ;i;H.,0.
On washing the fusion, sodium sulphate goes into the solu-
tion. It is also stated that hydrochloric acid gas acting on a
mixture of fluorspar and alumina at a high temperature will
produce aluminium fluoride :
AlA + sCaF^ + 6HC1 = 2AIF3 4- aCaCl, -1- 3H.,0.
The calcium chloride would be partly volatilized and the re-
mainder washed out of the fusion.
Hautefeuille§ obtained crystallized aluminium fluoride by
♦German Patent (D. R. P.), No. 35,212.
t Pogg- Annalen, 98, p. 488.
t Ann. de. Chim. et de Phys. [3], 61, p. 333; [3], 49, p. 79.
§Idem, [4], 4.P- iS3-
PREPARATION OF ALUMINIUM COMPOUNDS. 17I
passing hydrofluoric acid gas and steam together over red-hot
alumina.
Ludwig Grabau, of Hanover, bases his process of producing
aluminium on the reduction of aluminium fluoride (see Chap.
X.), which is prepared on a commercial scale by the following
ingenious methods :
* The process is based on the conversion of aluminium sul-
phate into fluoride by reaction with cryolite, the fluoride being
afterward reduced by sodium in such a manner that a double
fluoride of sodiuni and aluminium results, which is used over
again, thus forming a continuous process. The purest obtain-
able cryolite is used to start the process, after which no more
is needed, the material supplying the aluminium being its sul-
phate, which can be obtained cheaply in large quantities, and
almost perfectly pure. The process is outlined by the reac-
tions—
2 (AlFa-sNaF) + AUCSO*), = 4AIF3 + sNa.SO^
2AIF3 + sNa = AH AlFs.sNaF.
It is thus seen that theoretically the cryolite would be exactly
reproduced, but the losses and incomplete reactions unavoida-
ble in practice would cause less to be obtained, and necessitate
the continual addition of fresh cryolite ; since, however, it is
not desired to base the process on the continual use of cryo-
lite, because of the impurities in that mineral, an indirect pro-
cess is used, consisting of two reactions, in place of the first
given above, in which theoretically a larger quantity of cryolite
is finally obtained than is used to begin with. This is operated
by introducing fluorspar into the process, the base of which
goes out as calcium sulphate or gypsum, and so supplies the
fluorine needed.
In practice, a solution of aluminium sulphate is heated with
powdered fluorspar (obtained as pure as possible and further
cleaned by treatment with dilute hydrochloric acid). The
♦German Patent (D. R. P.), No. 48,535. March 8, 1889.
172 ALUMINIUM.
aluminium sulphate will not be entirely converted into fluoride,
as has been previously observed by Friedel,* but about two-
thirds of the sulphuric acid is replaced by fluorine, forming a
fluorsulphate of aluminium. This latter compound remains in
solution, while gypsum and undecomposed fluorspar remain as
a residue and are filtered out.
AlaCSO,)^-!- 2CaF, = Al^F.CSOi) +2 CaSOi.
This solution is concentrated and mixed with cryolite in such
proportion that the alkali in the latter is just equivalent to the
sulphuric acid in the fluor-sulphate. The mass is dried and
gnited, and the product washed and dried.
3AUF,(S0,) + 2(AlF3.3NaF) =8A1F3+ 3Na,S04.
On reduction with sodium, the 8 molecules of aluminium fluor-
ide, treated with sodium as by the reaction given, produce 4
molecules of the double fluoride. It is thus seen that after
allowing for reasonable losses in the process there is much .
more cryolite produced than is used, and the excess can be
very profitably sold as pure cryolite, being absolutely free from
iron or silica.
Grabau proposed to obtain his aluminium sulphate solution
directly from kaolin, by treatment with sulphuric acid, and thus
utilize this most abundant of the aluminous minerals. It is
claimed that aluminium fluoride of the greatest purity can be
thus manufactured at a less cost than pure alumina can be
made.
More recently the method of production has been varied as
follows:! To produce aluminium fluoride free from silicon and
iron, calcined clay or kaolin is stirred in excess into dilute hy-
drofluoric acid, a 12 per cent, solution of which is recommended.
The violent reaction ensuing is moderated by cooling, so that
the temperature does not exceed 95°. After a few minutes the
* Bull, de la Soc. Chimique [2], xxi, 241.
t German Patent No. 69,791, August 20, 1892.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 73
liquor is neutralized, as may be tested by a drop giving a pure
yellow with tropaolin. This neutrality is essential to ensure
the solution being free from silica. Further, this neutrality
cannot be obtained using uncalcined clay, nor with clay which
has been too highly heated. The clay must be calcined at a
certain determined temperature, which can only be learned by
experience. The hot, neutral solution is cooled to a moderate
temperature and filtered quickly, washing the residue with hot
water. On an average the equivalent of 95 per cent, of the hy-
drofluoric? acid used can be obtained in the form of dissolved
aluminium fluoride. The solution will be free from dissolved
silica, but may contain iron, lead, arsenic or other accidental
impurities. In order to separate out pure aluminium fluoride
from this solution, Grabau has patented the following method of
procedure :* The solution is first treated with sulphuretted hy-
drogen gas, which precipitates any lead, copper, arsenic, etc.,
which may be present, and reduces any ferric salt present to the
ferrous state. Any other reducing agent could also be used to
effect this. The solution is filtered and slightly acidified, so
that a test drop turns red with tropaolin. A neutral solution
holding hydrogen sulphide would in the subsequent cooHng de-
posit traces of iron sulphide. The acidified solution is then
str-ongly cooled in a receptacle, which may be of sheet alumin-
ium. There at once separates out crystalline, hydrated alu-
minium fluoride, AIF3.9H2O. It is best to start the crystalliza-
tion by dropping in a trace of the crystallized salt. As soon as
the crystallization commences the temperature rises ; when it
again sinks to 0° by continuing the cooling, the crystallization
is ended. The thick crystal liquor is separated on filters or in
a centrifugal machine, into mother liquor and crystals; the
latter are washed with ice-cold water. These crystals are free
from iron, but if the solution had not been previously reduced,
noticeable quantities of ferric fluoride would have been in them.
These crystals are easily dried and the water driven off by
gentle heating.
♦German Patent No. 70,155, August 20, 1892.
1 7 i ALUMINIUM.
IV.
The Preparation of Aluminium Sulphide.
Until the researches of M. Fremy, no other method of pro-
ducing aluminium sulphide was known save by acting on the
metal with sulphur at a very high heat. Fremy was the first
to open up a diflferent method, and it may be that his discov-
eries will yet be the basis of successful industrial processes. In
order to understand just how much he discovered, w? here give
all that his original paper contains concerning this sulphide.*
"We know that sulphur has no action on silica or boric ox-
ide, magnesia, or alumina. I thought that it might be possible
to replace the oxygen by sulphur if I introduced or intervened
a second affinity, as that of carbon for oxygen. These decom-
positions produced by two affinities are very frequent in chem-
istry ; it is thus that carbon and chlorine, by acting simultane-
ously on silica or alumina, produce silicon or aluminium
chloride, while either alone could not decompose it ; a similar
case is the decomposition of chromic oxide by carbon bisul-
phide, producing chromium sesquisulphide. Reflecting on
these relations, I thought that carbon bisulphide ought to act
at a high heat on silica, magnesia, and alumina, producing
easily their sulphides. Experiment has confirmed this view.
I have been able to obtain in this way almost all the sulphides
which until then had been produced only by the action of sul-
phur on the metals.
" To facilitate the reaction and to protect the sulphide from
the decomposing action of the alkalies contained in the por-
celain tube which was used, I found it sometimes useful to mix
the oxides with carbon and to form the mixture into bullets
resembling those employed in the preparation of aluminium
chloride. I ordinarily placed the bullets in little carbon boats,
and heated the tube to whiteness in the current of vaporized
* Ann. de Chim. et de Phys. [3], 38, p. 312.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 75
carbon bisulphide. The presence of divided carbon does not
appear useful in the preparation of this sulphide.
" The aluminium sulphide formed is not volatile ; it remains
in the carbon boats and presents the appearance of a melted
vitreous mass. On contact with water it is immediately de-
composed :
A1,S, + 3H,0 = Al,03 + 3H,S.
" The alumina is precipitated, no part of it going into solu-
tion. This precipitated alumina is immediately soluble in weak
acids. The clear solution, evaporated to dryness, gives no
trace of alumina. It is on this phenomenon that I base the
method of analysis.
" Aluminium sulphide being non-volatile, it is always mixed
with some undecomposed alumina. It is, in fact, impossible to
entirely transform all the alumina into sulphide. I have heated
less than a gramme of alumina to redness five or six hours in
carbon bisulphide vapor, and the product was always a mixture
of alumina and aluminium sulphide. The reason is that the
sulphide, being non-volatile and fusible, coats over the alumina
and prevents its further decomposition. The alumina thus
mixed with the sulphide, and which has been exposed to a red
heat for a long time, is very hard, scratches glass, and is in
grains which are entirely insoluble in acids. By reason of this
property I have been able to analyze the product exactly, for
on treating the product with water and determining on the one
hand the sulphuretted hydrogen evolved, and on the other the
quantity of soluble alumina resulting, I have determined the
two elements of the compound. One gramme of my product
contained 0.365 grm. of aluminium sulphide, or 36.5 per cent.,
the remainder being undecomposed alumina."
The composition of this sulphide was—
Aluminium °-i37 g™- = 37-5 pef cent.
Sulphur 0.228 "=62.5
0.365 " lOO.O "
1/6 ALUMINIUM.
The formula AI2S3 requires —
Aluminium 36.3 per cent.
Sulphur 63.7 "
The above is the substance of Fremy's investigations and
results. Reichel* next published an account of further experi-
ments in this line. He found that by melting alumina and sul-
phur together no reaction ensued. In the case of magnesia, the
sulphide was formed if carbon was mixed with the magnesia
and sulphur, but this change did not alter the alumina. Hydro-
gen gas passed over a mixture of alumina and sulphur likewise
gave negative results. Sulphuretted hydrogen passed over ig-
nited alumina did not succeed. By filling a tube with pure alu-
mina, passing in hydrogen gas and the vapor of carbon bisul-
phide, the heating being continued until carbon bisulphide
condensed in the outlet tube, and then hydrogen being passed
through until the tube was cold, a product was obtained con-
taining aluminium sulphide and undecomposed alumina.
In 1886, the writer made a series of experiments on the pro-
duction and reduction of aluminium sulphide. Alumina, either
alone or mixed with carbon or with carbon and sulphur, was
put in porcelain or carbon boats into a hard glass or porcelain
tube. This was then heated and vapor of carbon bisulphide
passed through it. The product was analyzed according to
Fremy's directions. The proportion of aluminium sulphide
obtained in the product varied from 13 to 40 per cent. The
best result was obtained at the highest heat — almost whiteness.
The presence of sulphur or carbon, or both together, mixed
with the alumina, did not promote to any degree the formation
of a richer product. The conditions for obtaining the best re-
sults seem to be high heat and fine division of the alumina to
facilitate its contact with the carbon bisulphide vapor. The
product was light-yellow when not mixed with carbon, easily
pulverized, and evolved sulphuretted hydrogen gas energetically
* Jahresb. der Chemie, 1867, p. 155.
PREPARATION OF ALUMINIUM COMPOUNDS. 1 77
when dropped into water. Since carbon bisulphide can now be
manfactured at a very low price, say 2 to 3 cents per lb., it is
not impossible that it may be found profitable to produce
aluminium from its sulphide. In such a case, large retorts
would be used, a stirring apparatus would facilitate the forma-
tion of a richer product, and the unused carbon bisulphide
could be condensed and saved.
M. Comenge,* of Paris, proposed to prepare aluminium sul-
phide by using a clay retort similar to those used in gas-works,
filling it one- half its length with charcoal or coke and the other
half with alumina. The retort being heated to rednesss, sul-
phur is introduced at the coke end, when in contact with the
carbon it forms carbon bisulphide, which acts upon the alumina
at the other end, producing the sulphide.
Messrs. Reillon, Montague, and Bourgerel f obtained a pat-
ent in England for producing aluminium, in which aluminium
sulphide is obtained by mixing powdered alumina with 40
per cent, of its weight of charcoal or lampblack and formed
into a paste with a sufficient quantity of oil and tar. This is
then calcined in a closed vessel and an aluminous coke ob-
tained. This is broken into pieces, put into a retort, and
treated with carbon bisulphide vapor. The inventors state
that the reaction takes place according to the formula
2 A1,0, + 3C + 3CS, = 4A1,S, -^ 6C0.
PetitjeanI states that if alumina is mixed with tar or turpentine
and ignited in a carbon-lined crucible, and the coke obtained
mixed intimately with sulphur and carbonate of soda and ig-
nited a long time at bright redness, there results a double sul-
phide of aluminium and sodium, from which aluminium can be
easily extracted.
It has been stated § that if aluminium fluoride is heated with
* English Patent, 1858, No. 461.
t English Patent, No. 4,756, March 28, 1887.
JPolytechnisches Central. Blatt., 1858, p. 888.
§ Chemical News, i860.
12
178 ALUMINIUM.
calcium sulphide, aluminium sulphide results. F. Lauterborn*
also makes the same claim in a patent twenty years later, but
the possibility of this reaction taking place is not yet beyond
question.
* German Patent (D. R. P.), No. 14,495 (1880).
CHAPTER VII.
THE MANUFACTURE OF SODIUM.
Some years ago, in order to treat fully of the metallurgy of
aluminium it would have been as necessary to accompany it
with all the details of the manufacture of sodium as to give the
details of the reduction of the aluminium, because the manu-
facture of the, former was carried on solely in connection with
that of the latter. But now sodium has come out of the list of
chemical curiosities, and has become an article of commerce,
used for many other purposes than the reduction of aluminium.
In fact, the last four years has seen the almost total extinction
of the sodium processes of producing aluminium. If it be asked
why such a chapter as this is still retained in a treatise on alu-
minium, the answer is that for thirty years aluminium was
made solely by its use; sodium is bound up with the history of
aluminium ; and it is not impossible, though perhaps improba-
ble, that some improved form of sodium process, in which me-
tallic sodium is produced and at once utilized in the one ope-
ration, may yet find a footing in the aluminium industry. For
these and other reasons which might be advanced, the methods
of producing sodium are yet of considerable interest to the
worker in aluminium, and are therefore retained, with the addi-
tion of a few recent processes.
Davy to Deville (1808-1855).
Sodium was first isolated by Davy by the use of electricity in
the year 1808.* Later, Gay Lussac and Thenard made it by
decomposing at a very high temperature a mixture of sodium
carbonate and iron filings, f In 1808, also, Curaudau an-
* Phil. Trans., :8o8.
fRecherches Physico-chimiques, 1810.
(179)
i8o
ALUMINIUM.
nounced that he had succeeded in producing potassium or
sodium without using iron, simply by decomposing their car-
bonates by means of animal charcoal. Briinner, continuing
this investigation, used instead of animal charcoal the so-called
black flux, the product obtained by calcining crude tartar from
wine barrels. He was the first to use the wrought-iron mer-
cury bottles. The mixture was heated white hot in a furnace,
the sodium volatilized, and was condensed in an iron tube
screwed into the top of the flask, which projected from the fur-
nace and was cooled with water. In Brunner's experiments he
only obtained three per cent, of the weight of the mixture as
metallic sodium, the rest of the metal being lost as vapor.
Donny and Mareska gave the condenser the form which with
a few modifications it retains to-day.
It was of iron, 4 millimetres thick, and
was made in the shape of a book,
having a length of about 100 centi-
metres, breadth 50, and depth 6 (see
Fig. 9). This form is now so well
known that a further description is
unnecessary. With this condenser the
greatest difficulty of the process was
removed, and the operation could be
carried on in safety. This apparatus
was devised and used by Donny and Mareska in 1854, with the
supervision of Deville.
FlQ. 9.
Deville' s Improvements at Javel (1855).
The following is Deville's own description of the attempts
which he made to reduce the cost of producing sodium. As
far as we can learn these experiments were commenced in 1854,
but the processes about to be given are those which were car-
ried out at Javel, March to June, 1855. As the description
contains so many allusions to the difficulties met not only in pro-
ducing but also in handling and preserving sodium, its perusal
is yet of value to all concerned in this subject, although the
THE MANUFACTURE OF SODIUM. l8l
actual methods here described have been superseded by much
more economical ones.
Properties of sodium. — "The small equivalent of sodium and
the low price of sodium carbonate should long since have
caused it to be preferred to potassium in chemical operations,
but a false idea prevailed for a long time concerning the diffi-
culties accompanying the reduction. When I commenced
these researches the cost of sodium was at least double that of
potassium. In this connection I can quote from my memoir
published in the Ann. de Chim. et de Phys., Jan., i, 1855 : "I
have studied with care the preparation of sodium and its prop-
erties with respect to oxygen and the air, in order to solve the
difficulties which accompany its reduction and the dangers of
handling it. In this later respect, sodium is not to be com-
pared to potassium. As an example of how dangerous the
latter is, I will relate that being used to handle sodium and
wishing once to replace it with potassium, the simple rubbing
of the metal between two sheets of paper sufficed to ignite it
with an explosion. Sodium may be beaten out between two
sheets of paper, cut and handled in the air, without accident if
the fingers and tools used are not wet. It may be heated with
impunity in the air, even to its fusing point, without taking fire,
and when melted, oxidation takes place slowly, and only at the
expense of the moisture of the air. I have even concluded
that the vapor alone of sodium is inflammable, but the vivid
combustion of the metal can yet take place at a temperature
which is far below its boiling point, but at which the tension of
the metallic vapors has become sensible." I will add to these
remarks that sodium possesses two considerable advantages :
it is obtained pure at the first operation, and, thanks to a
knack which I was a long time in finding out, the globules of
the metal may be reunited and treated as an ordinary metal
when melting and casting in the air. I have thus been able to
dispense with the distillation of the raw products in the manu-
facture— an operation which had come to be behaved neces-
sary, and which occasioned a loss of 50 per cent, or so on the
1 82 ALUMINIUM.
return, without appreciable advantage to the purity of the
metal. The manufacture of sodium is in no manner encum-
bered by the carburetted products, or perhaps nitrides, which
are very explosive, and render the preparation of potassium so
dangerous. I ought to say, however, that by making potas-
sium on a large scale by the processes I am about to describe
for sodium, Rousseau Bros, have diminished the dangers of its
preparation very much, and practice the process daily in their
chemical works.
Method employed. The method of manufacture is founded
on the reaction of carbon on alkaline carbonate. This method
has been very rarely applied to sodium, but is used every day
for producing potassium. Brunner's process is, in fact, very
difficult to apply, great trouble being met, especially in the
shape of condenser used. It is Donny and Mareska who have
mastered the principles which should guide in constructing
these condensers.
Composition of mixtures used. The mixture which has given
me excellent results in the laboratory is :
Sodium carbonate 717 parts.
Wood charcoal 1 75 "
Chalk 108 "
1000
Dry carbonate of soda is used, the carbon and chalk pulver-
ized, the whole made into a paste with oil and calcined in a
crucible. The end of a mercury bottle, cut off, serves very
well, and can be conveniently closed. Oil may be used alto-
gether in place of charcoal, in which case the following pro-
portions are used :
Sodium carbonate 625 parts.
Oil 280 "
Chalk 95 "
That a mixture be considered good, it should not melt at the
temperature at which sodium is evolved, becoming liquid at
THE MANUFACTURE OF SODIUM. 1 83
this point and so obstructing the disengagement of the gas.*
But it should become pasty, so as to mold itself evenly against
the lower side of the iron vessel in which it is heated. The
considerable latent heat required by carbonic oxide and sodium
in assuming the gaseous state, is one cause of cooling which re-
tards the combustion of the iron. When soda salt is intro-
duced in place of dried soda crystals, the mixture, whatever its
composition, always melts, the gases making a sort of ebulli-
tion, the workmen saying that the apparatus " sputters." This
behavior characterizes a bad mixture. It has been demon-
strated to me that the economy made at the expense of a
material such as carbonate of soda, the price of which varies
with its strength in degrees, and which forms relatively a small
portion of the cost of sodium, is annulled by a decrease of 20 to
25 per cent, in the return of sodium. The oil used ought to be
dry and of long flame. It acts as a reducing agent, and also
furnishes during the whole operation hydrogenous gases, and
even, towards the close, pure hydrogen, which help to carry
the sodium vapor rapidly away into the condenser, and to
protect the condensed metal from the destructive action of the
carbonic oxide. Oil renders a similar service in the manu-
facture of zinc. The role of the chalk is easy to understand.
By its infusibility it decreases the liability of the mixture to
melt. Further it gives off carbonic acid, immediately reduced
by the carbon present to carbonic oxide. Now, the sodium
ought to be carried rapidly away out of the apparatus, because
it has the property of decomposing carbonic oxide, which is
simultaneously formed, within certain limits of temperature,
especially if the sodium is disseminated in little globules and
so presents a large surface to the destructive action of the gas.
It is necessary, then, that the metallic vapors should be rapidly
conducted into the condenser and brought into the liquid state
* It seems plain, however, granting that vapors would be evolved most freely from
2. perfectly infusible charge, that a pasty condition, such as is recommended in the
next sentence, would be the worst possible state of the charge for evolving gas, being
manifestly inferior to a completely fluid bath.— J. W. R.
1 84 ALUMINIUM.
— not into that state comparable to "flowers of sulphur," in
which the metal is very oxidizable because of its fine division.
A rapid current of gas, even of carbonic oxide, actively carries
the vapors into the condenser, which they keep warm and so
facilitate the reunion of the globules of sodium. At La
Glaciere and Nanterre a mixture was used in which the, pro-
portion of chalk, far from being diminished, was, on the con-
trary, increased. The proportions used were —
Sodium carbonate 40 kilos = 597 parts.
Oil 18 " =269 "
Chalk 9 " =134 "
67 1000
This quantity of mixture ought to give 9.4 kilos of sodium,
melted and cast into ingots, without counting the metal divided
and mixed with foreign materials, of which a good deal is
formed. This return would be one-seventh of the weight of
the mixture, or one-quarter of the sodium carbonate used.
Use of these mixtures. The carbonate of soda, charcoal, and
chalk ought to be pulverized and sieved, well mixed and again
sieved, in order to make a very intimate mixture ; the mixture
ought to be used as soon as possible after preparing, that it
may not take up moisture. The mixture may be put just as it
is into the apparatus where it should furnish sodium, but it may
very advantageously be previously calcined so as to reduce its
volume considerably, and so permit a greater weight being put
into the same vessel. I believe that whenever this calcination
may be made with economy, as with the waste heat of a fur-
nace, a gain is made by doing so, but the procedure is not in-
dispensable. However, the utility of it may be judged when
it is stated that a mercury bottle held two kilos of non-calcined
mixture, but 3.6 kilos were put into one when previously cal-
cined. These two bottles heated in the same fire for the same
time gave quantities of sodium very nearly proportional to the
weight of soda in them. In working under the direction of a
good workman, who made the bottles serve for almost four
THE MANUFACTURE OF SODIUM. 1 85
operations, I have been able to obtain very fine sodium at as
low a price as 9.25 francs per kilo. ($0.84 per pound). In the
manufacture of sodium by the continuous process, where the
materials may be introduced red hot into the apparatus, this
preliminary calcination is a very economical operation.
Apparatus for reducing, condensing, and heating. — M. Briin-
ner had the happy idea of employing mercury bottles in manu-
facturing potassium ; thus the apparatus for reduction was in the
hands of any chemist, and at such a low price that any one has
been able to make potassium without much trouble. These
bottles are equally suitable for preparing sodium, and the
quantity which may be obtained from such apparatus and the
ease with which they are heated, are such that they might have
been used a long time for the industrial manufacture, except
for two reasons which tend to increase the price of these bottles
continually. For some time a large number of bottles have
been sent to the gold workers of Australia and California, also
large quantities have been used in late years in preparing the
alkaline metals ; these two facts have diminished the number to
such a point that from 0.5 or i franc the price has been raised
to 2.5 or 3 francs. It has thus become necessary to replace
them, which has been done by substituting large wrought-iron
tubes which have the added advantage of being able to be
worked continuously. I will first describe the manufacture in
mercury bottles, which may still be very advantageously used
in the laboratory, and afterwards the continuous production in
large iron cylinders as now worked industrially.
Manufacture in mercury bottles. — The apparatus needed is
composed of a furnace, a mercury bottle, and a condenser.
The form of furnace most suitable is a square shaft, C (Fig.
10), the sides of which are refractory brick, while the grate G
ought to have movable grate bars, the furnace being connected
above with a chimney furnishing good draft. The flue F, con-
necting with the chimney, should have a damper, R, closing
tightly, and should lead exactly from, the centre of, the top of
the shaft, thus dividing the draft equally all over the grate.
1 86
ALUMINIUM.
Coke is charged through lateral openings at 0. A small open-
ing closed by a brick should be left a short distance above the
grate bars, in order to poke down the coke around the bottle
should it not fall freely. The space between the grate and
bottle should always be full of fuel in order to keep the iron of
the bottle from being burnt. In front of. the furnace is a square
opening, P, closed with an iron plate, which has a hole in it by
which the tube T issues from the furnace.
The mercury bottle is supported on two refractory bricks,
KK, cut on their top side to the curve of the bottle. These
Fig. 10.
should be at least 20 centimetres high to maintain between the
grate and the bottle a convenient distance. The illustration
gives the vertical dimensions correctly, but the horizontal
dimensions are somewhat shortened. There should be at least
12 centimetres between the bottle and sides of the furnace.
However, all these dimensions should vary with the strength of
the chimney draft and the kind of fuel used ; the furnace
should be narrower if the draft is very strong and the coke
dense. The iron tube T, which may conveniently be made of
a gun barrel, is either screwed into the bottle or it may be
simply fitted and forced into place, provided it hold tightly
THE MANUFACTURE OF SODIUM. 1 87
enough. It should be about 5 to 6 centimetres long, and
should project scarcely i centimetre from the furnace. The
end projecting should be tapered off in order to fit closely into
the neck of the condenser.
The condenser is constructed with very little deviation from
that given by Donny and Mareska (see Fig. 9, p. 180). I
have tried my best to make this apparatus as perfect as
possible, but have always reverted to the form described by
those authors ; yet even the very small differences I have made
are indispensable and must be rigidly adhered to if it is wished
to get the best results obtainable. Two plates of sheet iron, 2
to 3 millimetres thick, are taken and cut into the shape indi-
cated by Fig. II. One plate. A, remains flat except at the
point C, where it is drawn by hammering into a semi-
cylindrical neck of about 25 millimetres inside diameter. This
Fig. II.
iiiiii 111!
■corresponds with a similar neck in the other plate, so that on
joining the two there is a short cylinder formed. The edges of
the plate A are raised all around the sides about 5 to 6 milli-
metres, so that when the two plates are put together the longi-
tudinal section from £> to Cis as in Fig. 12. As to the end,
in one form the edge was not turned up, leaving the end open
as in Fig. 13. Another form, which I use when wishing to let
the sodium accumulate in the condenser till it is quite full, is
made by turning up the edge at the end all but a small space
left free, thus giving the end the appearance of Fig. 14, this
-device also being shown in Fig. 11. The gas evolved during
1 88 ALUMINIUM.
the reaction then escapes at the hole 0. The most rational
arrangement of the apparatus is that shown in Fig. 15. In this
condenser the lower part, instead of being horizontal, is in-
clined, and the end having two openings, O and 0' , the sodium
trickles out at the lower one as it condenses, while the gas es-
capes by the slightly larger upper opening. In placing the
plates together, the raised edges are washed with hme so as to
form a good joint with the flat plate, and the plates are kept
together by strong pressure grips.
To conduct the operation, the bottles are filled entirely with
mixture, the tube T adjusted, and then placed on the two sup-
ports, there being already a good bed of fire on the grate. The
front is put up, the shaft filled with coke, and the damper
opened. The gases disengaged from the bottle are abundant,
of a yellow color ; at the end of half an hour white fumes of
carbonate of soda appear. The condenser should not yet be
attached, but it should be noted if any sodium condenses on a
cold iron rod pushed into the tube, which would be indicated
by its fuming in the air. As soon as this test shows that sodium
is being produced, the condenser is attached and the fire kept
quite hot. The condenser soon becomes warm from the gases
passing through it, while the sodium condenses and flows out
at the end D (Fig. 15). It is received in a cast-iron basin L,
in which some non-volatile petroleum is put. When at the end
of a certain time the condenser becomes choked, it is replaced
by another which has been previously warmed up to 200° or
300° by placing it on top of the furnace. If the closed con-
denser is used, care must be taken to watch when it becomes
full, on the point of running from the upper opening, and the
condenser then replaced and plunged into a cast-iron pot full
of petroleum at a temperature of 150°. The sodium here
melts at the bottom of this pot and is ladled out at the end of
the day. The oil is generally kept up to 150° by the hot con-
densers being plunged in constantly. The pot ought to have
a close cover, to close it in case the oil takes fire ; the extinc-
tion of the fire can thus be assured and no danger results. If
THE MANUFACTURE OF SODIUM. 1 89
the oil fires just as a condenser is being introduced, the sodium
is run out in the air without igniting, the only drawback being
that the condenser must be cleaned before using again. This
method occasions a large loss of oil, however, and has been
completely abandoned for the other form of condensers. When
the operation proceeds well only pure sodium is obtained, the
carbonized products which accompany in so provoking a man-
ner the preparation of potassium not occurring in quantity
sufficient to cause any trouble. Before using a condenser a
second time it is put on a grating over a basin of petroleum
and rubbed with a chisel-pointed tool in order to remove any
such carbonized products. From time to time this material is
■collected, put into a mercury bottle, and heated gently. The
oil first distils, and is condensed in another cold bottle. The
fire is then urged, a condenser attached, and the operation pro-
ceeds as with a fresh charge, much sodium being thus recov-
ered.
The raw sodium is obtained from the bottles in quantities
of over half a kilo ; it is perfectly pure, dissolving in absolute
alcohol without residue. It is melted and moulded into ingots
just as lead or zinc. The operation I have described is exe-
cuted daily, and only once has the sodium ignited. To prevent
such accidents it is simply necessary to keep water away from
the apparatus. The reduction of carbonate of soda and the
production of sodium are such easy operations that when tried
by those conversant with the manufacture of potassium or who
have read about the difficulties of the production of sodium,
success is only gained after several attempts — the failure being
due solely to excess of precautions. The reduction should be
carried on rapidly, so that a bottle charged with two kilos of
rriixture may be heated and emptied in, at most, two hours. It
is unnecessary to prolong the operation after the yellow flame
stops issuing from the condenser, for no more sodium is ob-
tained and the bottle may frequently be destroyed. The
temperature necessary for the reduction is not so high as it has
teen so far iiriagined. M. Rivot, who has assisted in these ex-
I go ALUMINIUM.
periments, thinks that the bottles are not heated higher than
the retorts in the middle of the zinc furnaces at Vielle Mon-
tagne. I have been even induced to try cast-iron bottles, but
they did not resist the first heating, without doubt because they
were not protected from the fire by any luting or covering. But
I was immediately successful in using cast-iron bottles decar-
burized by the process used for making malleable castings.
The mercury bottles heated without an envelope ought to serve
three or four operations when entrusted to a careful workman.
Besides all these precautions, success in this work depends
particularly on the ability and experience of the workman, who
can at any time double the cost of the sodium by carelessness
in managing the fire. _
Continuous manufacture in cylinders. It might be thought
that by increasing proportionately in all their parts the dimen-
sions of the apparatus just described, it would be easy to pro-
duce much larger quantities of sodium. This idea, which
naturally presented itself to me at once, has been the cause of
many unfruitful attempts, into the details of which I will not
enter. I must, however, explain some details which may ap-
pear insignificant at first sight, but which were necessitated
during the development of the process. For instance, it will
perhaps look irrational for me to keep the same sized outlet
tubes and condensers that were used with the mercury bottles,
for tubes five times as large ; but I was forced to adopt this
arrangement after trying the use of tubes and condensers of all
sizes ; indeed, it is fortunate for the success of the operation
that this was so, for it became very injurious to the workmen
to handle the large and weighty apparatus in the face of a large
sodium flame.
The mixture of sodium carbonate and carbon is made in the
manner already described. I would say again that a previous
strong calcination of the materials presents a great advantage^
not only because it permits putting a much larger weight into
the retorts at once, but also that, being more compact, the mix-
ture will not rise as powder and be violently thrown out of the
THE MANUFACTURE OF SODIUM.
191
Strongly-heated retorts. The mixture should also be calcined
as needed, and used to fill the tubes while still red hot. When
cold, uncalcined mixture is used, it is put into large cartridges
of thick paper or canvas, 8 centimetres diameter and 35 cen-
timetres long.
The furnace and tubes are shown in section in Fig. 16. The
tubes T are 120 centimetres long, 14 centimetres inside
diameter, and 10 to 12 millimetres in thickness. They are
formed from one piece of boiler iron, bent and welded along
Fig. 16.
one side. The iron plate P which closes one end is about 2
centimetres thick, and pierced on one of its edges quite close
to the side of the cylinder by a hole in which is screwed or
fitted an iron tube, Z, 5 to 6 centimetres long and 15 to 20
millimetres inside diameter, and tapering off at the end to fit
into the condenser neck. The other end of the tube is closed
by an iron plug, 0, terminated by a knob. The welded side of
the tube is kept uppermost. These iron tubes should not, like
the mercury bottles, be heated in the bare fire ; it is necessary
to coat them with a resistant luting which is itself enveloped by
a refractory jacket i centimetre thick, 22 centimetres interior
192 ALUMINIUM.
diameter, and the same length as the retorts. This protection
is commenced by plastering the retorts over with a mixture of
equal parts of raw clay and stove ashes, which have been made
into a paste with water and as much sand worked into the mix-
ture as it will take without losing its plasticity, also adding
some horse manure. This luting should be dried slowly, and
the tube thus prepared is introduced into the refractory jacket,
the open space between the two being filled with powdered
refractory brick. Finally, luting is put on the iron plate P, so
that no part of it is exposed to the flame.
The furnace I have used is a reverberatory, but I do not re-
commend its use without important modifications, because it
does not realize all the conditions of easy and economic heat-
ing. The grate is divided into two parts by a little wall of re-
fractory brick, on which the middle of the reduction cylinders
rests. The tubes are thus seen to be immediately over the bed
of fuel. The top of the bridge is a little higher than the upper
edge of the cylinders, this and the very low arch making the
flame circulate better all around the tubes. A third cylinder
might easily be placed above these two, and be heated satis-
factorily, without any more fuel being burnt. This reverbera-
tory receives on its bed the mixtures to be calcined, placed in
cast-iron or earthen pots according to their composition.
When the furnace is kept going night and day producing
sodium, the temperature rises on the bed to clear cherry-red,
and experience has shown that other reducing cylinders might
be placed there, under such conditions, and be heated suf-
ficiently for the reduction.
All that I have said of the manufacture of sodium in mercury
bottles applies equally to its manufacture in cylinders. The
only difference consists in the charging and discharging, and I
have only to add several precautions to be taken. On intro-
ducing the cartridges containing uncalcined mixture, only 8 to
9 kilos can be heated at once ; double as much can be used of
previously-calcined mixture. The plug 0 is put in place, not
so tightly that it cannot easily be taken out again ; a little
THE MANUFACTURE OF SODIUM. 1 93
luting stops all leakages which show themselves. The reduc-
tion lasts about four hours. When it is finished, a little water is
thrown on the plug 0, and it is easily loosened and removed.
On looking into the cylinder, the cartridges are seen to have
kept their shape, but have shrunken so much that their diameter
is only about 2 to 3 centimetres ; they are very spongy. This
shows that the mixture has not melted ; the remainder is prin-
cipally lime and carbon, and free from sodium carbonate.
While opening the cylinder, a bright-red-hot iron is thrust into
the outlet tube L, to keep dirt from getting into it, and it is
kept in until the charging is finished. The cartridges are put
in by means of semi-cylindrical shovels. The sudden heating
of the mixture disengages soda dust from uncalcined mixtures,
which is very disagreeable to the workmen. The cylinders are
closed, and when the sodium flame appears at the outlet tube
the condenser is attached, and the operation proceeds as
already described.
The envelopes of the cylinders are thick enough to prevent
the distillation of the sodium being in any way affected by the
accidental causes of cooling the fire. So when fresh fuel is
charged or the door of the reverberatory is opened, causing the
draft to cease almost entirely in the fire-place, the operation
should not suffer by these intermittences, provided.that they are
not too long prolonged. In short, when operating in cylinders,
the production of sodium is easier, less injurious to the work-
men, and less costly in regard to labor and fuel than when
working with mercury bottles. At times, after working a fort-
night with many interruptions dangerous for the apparatus, my
experiment has been suddenly ended. The furnace was intact ;
the envelopes of the tubes were split open, and the luting on
the tubes found to be compact and coherent, but without traces
of fusion, showing perfect resistance. The iron tubes mean-
while had not suffered inside or out, and seemed as though
they would last indefinitely. I attribute this success to the par-
ticular care given to the composition of the jackets, and to the
perfection with which the tubes had been welded. Only on
13
194 ALUMINIUM.
one of the tubes was a very slight crack found, on a part not
the most highly heated, and not sufficient to cause the tube to
be discarded.
Tissier Bros.' method of procedure. (1856). As related in
the historical treatment of the subject (p. 13), Deville charged
the Tissier Bros, with appropriating from him the process for
the continuous production of sodium in cylinders, which, as
just given, was devised during the experiments at Javel. On
the other hand, the Tissier Bros, asserted their right to the
process, patenting it, and using it in the works started at Rouen
in the latter part of 1855. The following details are taken
from Tissier's " Recherche de 1' Aluminium," only such being
selected as supplement Deville's description, which has just
been given.
The sodium carbonate is first well dried at a high temper-
ature, then mixed with well-dried pulverized charcoal and chalk,
ground to the finest powder, the success of the operation de-
pending on the fineness of this mixture. The proportions of
these to use are various. One simple mixture is of
Sodium carbonate 566
Coal 244
Chalk 95
Coke 95
1000
Another contains —
Sodium carbonate 615
Coal 277
Chalk 108
1000
The addition of chalk has the object of making the mixture
less fusible and more porous, but has the disadvantage that the
residue remaining in the retort after the operation is very im-
pure, and it is impossible to add any of it to the succeeding
charge ; and also, some of it being reduced to caustic lime
forms caustic alkali with some sodium carbonate, which is then
THE MANUFACTURE OF SODIUM.
195
lost. WheD the mixture is well made it is subjected to a pre-
limiinary calcination. This is done in cast-iron cylinders, two
of which are placed side by side in a furnace and heated to
redness (see Fig. 17). This is continued till all the moisture,
carbonic acid, and any carburetted hydrogen from the coal,
cease coming off. The mass contracts, becomes white and
somewhat dense, so that a larger amount of the mixture can
now be treated in the retorts where the sodium is evolved. As
soon as the outcoming gases burn with a yellow flame, showing
Fig. 17.
sodium coming ofT, the calcination is stopped. The mixture is
then immediately drawn out on to the stone floor of the shop,
where it cools quickly and is then ready for the next operation.
This calcination yields a mixture which without any previous
reactions is just ready to evolve sodium when brought to the
necessary temperature. This material is made into a sort of
cylinder or cartridge and put into the decomposition retorts
(see Fig. 16). The charging should be done quickly. The
final retorts are of wrought-iron, since cast-iron would not
stand the heat. At each end this retort is closed with wrought-
iron stoppers and made tight with fire-clay. Through one
stopper leads the pipe to the condenser, the other stopper is
the one removed when the retort is to be recharged. These
retorts are placed horizontally in rows in a furnace. Usually
four are placed in a furnace, preferably heated by gas, such as
the Siemens regenerative furnace or Bicheroux, these being
196 ALUMINIUM.
much more economical. In spite of all these precautions the
retorts will be strongly attacked, and in order to protect them
from the destructive action of a white heat for seven or eight
hours they are coated with some kind of fire-proof material.
The best for this purpose is graphite, which is made into cylin-
ders enclosing the retorts, and which can remain in place till
the furnace is worn out. These graphite cylinders not only
protect the iron retorts, but prevent the diffusion of the gas-
eous products of the reaction into the hearth, and so support
the retorts that their removal from the furnace is easily accom-
plished. Instead of these graphite cylinders the retorts may
be painted with a mixture that melts at white heat and so en-
amels the outside. A mixture of alumina, sand, yellow earth,
borax, and water-glass will serve very well in many cases. We
would remark that the waste gases from this furnace can be
used for the calcining of the mixture, or even for the reduction
of the aluminium by sodium, where the manufacture of the
former is connected with the making of the sodium.
As for the reduction of the sodium, the retort is first heated
to redness, during which the stopper at the condenser end of
the retort is left off. The charge is then rapidly put in, and the
stopper at once put in place. The reaction begins almost at
once and the operation is soon under full headway, the gases
evolved burning from the upper slit of the condenser tube with
a flame a foot long. The gases increase in volume as the
operation continues, the flame becoming yellower from sodium
and so intensely bright as to be insupportable to look at. Now
has come the moment when the workman must quickly adapt
the condenser to the end of the tube projecting from the retort,
the joint being greased with tallow or parafHn. The sodium
collects in this in a melted state and trickles out. The length
of the operation varies, depending on the intensity of the heat
and the quantity of the mixture ; a charge may sometimes be
driven over in two hours, and sometimes it takes eight. We
can say, in general, that if the reaction goes on quickly a some-
what larger amount of sodium is obtained. The higher the
THE MANUFACTURE OF SODIUM. 1 97
heat used, however, the quicker the retorts are destroyed. The
operation requires continual attention. From time to time, a
workm-an with a prod opens up the neck of the condenser,
but if care is not taken the metal overflows ; if this happens,
the metal overflowing is thrown into some petroleum, while
another man replaces the condenser with an empty one. The
operation is ended when the evolution of gas ceases and the
flame becomes short and feeble, while the connecting tube be-
tween the retort and condenser keeps clean and does not stop
up. As soon as this occurs, the stopper at the charging end
is removed, the charge raked out into an iron car, and a new
charge being put in, the operation continues. After several
operations the retorts must be well cleaned and scraped out.
The sodium thus obtained is in melted bits or drops, mixed
with carbon and sodium carbonate. It must, therefore, be
cleaned, which is done by melting it in a wrought-iron kettle
under paraffin with a gentle heat, and then casting it into the
desired shapes. The sodium is kept under a layer of oil or
any hydrocarbon of high boiling point containing no oxygen.
Tissier gives the reaction as —
Na2C03+2C=3CO+2Na.
The sodium is condensed, while the carbonic oxide, carrying
over some sodium, burns at the end of the apparatus. This
would all be very simple if the reaction of carbonic oxide on
sodium near the condensing point did not complicate matters,
producing a black, infusible deposit of sodium monoxide
(Na^O) and carbon, which on being melted always give rise to
a loss of sodium.
Deville's Improvements at La Glacier e (1857).
At this works Deville tried the continuous process of manu-
facturing sodium in cylinders on a still larger scale, with the fol-
lowing results, as described by Deville himself: —
" We made no change in the composition of the mixtures used
198 ALUMINIUM.
from those already described, or in the form or size of the iron
tubes or the method of condensation ; but we worked with six
cylinders at a time in a furnace similar to the puddling furnaces
of M. Guadillot, the tubes being protected by refractory envel-
opes. The cylinders were so arranged on the hearth that the
flame bathed all parts of their surface. A low brick wall ex-
tends down the centre of the hearth, supporting the middle of the
cylinders, which extend across it. The hearth is well rammed
with refractory sand, and the space between it and the bottom
of the cylinder serves as a passage-way for most of the flame.
" Our six cylinders worked satisfactorily for five days. We
were able to observe that they were all heated with remarkable
uniformity, and that the heat was sufficient all round them. It
also appeared that the rear end of the cylinders required only
a hermetic seal. Indeed, as soon as the operation was well
under way and sodium distilling off, some of it condensed and
oxidized in the cool parts of the apparatus, forming a sort of
plug of carbonate and carbides of sodium, which the vapor and
gases could no longer penetrate. We were thus able for a
long time to distil sodium away from one of our tubes which
was entirely opened at the rear.
" This new furnace worked so well that we were hopeful of
complete success, when an accident happened which compelled
the stopping of the experiment. The iron tubes had been
ordered 1.20 metres long, the size of the hearth calculated ac-
cordingly, but they were delivered to us only 1.05 metres long.
We made use of these, with the result that the rear ends be-
came red-hot during the operation and allowed sodium vapors
to leak through. These leaked through the luting, and escap-
ing into the furnace, melted the envelopes very rapidly.
"In another attempt, in which this fault was avoided, we were
unsuccessful because the envelopes gave way at the first heat-
ing up, both they and the iron tubes being of inferior quality.
We were considerably inconvenienced by the failure of these
experiments, which caused considerable expense and gave no
very definite results. Just then a new sort of apparatus was
THE MANUFACTURE OF SODIUM. 1 99
devised, a description of which is given later on. It will be
seen that we were compelled to employ tubes of very small
value, so that their destruction in case of accident involved no
great loss, and to heat each one by an independent fire, so that
the stoppage or destruction of one cylinder would not necessitate
the stoppage or endanger the safety of the neighboring ones."
Cast-iron vessels. Deville tried at La Glaciere, as well as at
Javel, to utilize cast-iron vessels for producing sodium. Deville
states the difficulties which caused their use to be unsuccessful
to be as follows :
"The result was always unfavorable. Sodium is obtained, but
as soon as its production becomes rapid the vessel melts and
the operation is quickly ended. This follows because the tem-
perature necessary for the production of the metal is far from
being sufficient for producing it in large quantities at once ; and
we know that this is the one condition for condensing the so-
dium well and obtaining it economically. This observation led
me to think that by diminishing very much the temperature of
the furnace, large apparatus of cast-iron with large working
surface could be used, thus making at a time a large amount of
metallic vapor which could be condensed in recipients of ordi-
nary size. The whole large apparatus would thus have the out-
put of a smaller one worked at a higher temperature. My ex-
perience has shown me that in large-sized tubes heated to a
low temperature there is formed in a given time about as much
sodium as from a single mercury bottle at a much higher heat.
This is the reason why larger condensers are not necessary
with the larger tubes. Before knowing this fact, I tried a large
number of useless experiments to determine the size of con-
densers suitable for large apparatus. It is on this principle
that I have long been endeavoring to make sodium without
working at high temperatures, and using less costly and more
easily protected apparatus."
Improvements used at Nanterre (1859).
The method used here was exactly that already described,
200 ALUMINIUM.
the improvements being solely in details of the apparatus.
These are described by Deville as follows : —
" The experiments made at Javel and the continuous process
used at Glaciere have shown us in the clearest manner the ab-
solute necessity of efficient protection for the iron cylinders, for
without this protection the method cannot be practiced with
economy. Further, experiments in this direction are very
costly, for the failure of a tube stops the working of a large
number of cylinders, and often compromises the brick-work of
the furnace itself. We therefore came to the conclusion that
for making the small quantity of sodium we required, 300 to 500
kilos a month, it would be better to employ smaller apparatus,
independent of each other and easy to replace.
" The iron tubes are made of thinner iron and at very little ex-
pense, by taking a sheet of iron, curving it into a cylinder and
riveting the seam. This tube resembles very closely those
used at Javel, shown in Fig. 16, but of smaller dimensions. It
is closed at each end by cast-iron plugs, one of which has a
hole for the outlet tube. These cylinders are filled with sodium
mixture and placed in furnaces of the form of Fig. 10, except it
is necessary to have openings in the back and front of the fur-
nace so that the cast-iron plugs closing the cylinders may be
outside, to prevent their melting. We used coke at first for
fuel, fed around the cylinders, but M. Morin has since placed the
tubes out of direct contact with the fuel, uses soft coal, and heats
the tubes by contact with the flame and by radiation. In the
latest form used, two cylinders are placed in each furnace, and,
in general, they serve for two or three operations. All that has
been said in connection with the manufacture in mercury bot-
tles is immediately applicable to the manufacture in cylinders
of this kind, the capacity of which may vary from two to six or
eight litres, without any change in the manner of using them.
We have, however, adopted altogether condensers of cast-iron.
The neck is cylindrical and belongs only to one-half of the ap-
paratus, the neck end of the other plate being beveled and fit-
ting closely against a recess in the other plate."
THE MANUFACTURE OF SODIUM. 20I
The foregoing shows the sodium industry as it was perfected
by Deville, in 1859, and as it remained for twenty-five years
without sensible change. The cost of sodium by this process
is stated to have been, in 1872, as follows: —
Manufacture of one kilo of sodium.
Soda 9.35 kilos @ 32 fr. per 100 kilos = 3 fr. 9 cent.
Coal 74.32 " " 1.40" " " " = I " 4 "
Wages 3 " 73 "
Expenses 3 " 46 "
Total 1 1 fr. 32 cent.
which is equal to $1 per lb. The larger part of the expense
account is the cost of retorts or tubes in which the operation
takes place, and which are so quickly destroyed that the re-
placing of them forms nearly one-quarter of the cost of the
metal.
Minor Improvements (185 9- 1888).
An experiment made by Deville in 1864* is of considerable
interest in connection with some more recent processes. Guy
Lussac and Thenard having observed that caustic potash is re-
duced by iron, Deville took a mercury bottle with an aperture
above and one below, to which was fitted an iron tube and a
sodium condenser. Finely divided iron, reduced by hydrogen,
was put into the bottle, and when red hot, caustic soda was in-
troduced through the upper aperture. The iron was strongly
acted upon, and in less than 20 minutes Deville obtained y^ a
kilo of pure sodium. The reduction was stopped by a mixture
of soda and iron oxide filling up the lower opening. The ar-
rangement and reactions suggest strongly some later processes.
Why Deville did not continue on this line, I cannot say.
R. Wagnerf uses paraffin in preference to paraffin oil in
which to keep the sodium after making it. Only pure paraffin,
which has been melted a long time on a water-bath, and all its
water driven off, can be used. The sodium to be preserved is
* Lef ons de Chemie, 1864-5, P- 336- + Dingier, 1883, p. 252.
202 ALUMINIUM.
dipped in the paraffin melted on a water-bath, and kept at no
higher heat than 55° C, and the metal is thereby covered with a
thick coat of paraffin which protects it from oxidation, and may
then be put up in wooden or paper boxes. When the metal is
to be used, it is easily freed from paraffin by simply warming
it, since sodium melts at 95° to 96° C, and the paraffin at 50°
to 60°.
The reduction of potassium carbonate by carbon requires a
much less degree of heat than that of sodium carbonate, and
therefore many attempts have been made to reduce potassium
and sodium together, under circumstances where sodium alone
would not be reduced. Dumas* added some potassium car-
bonate to the regular sodium mixture; and separated the
sodium and potassium from each other by a slow, tedious oxi-
dation. R. Wagnerf made a similar attempt. He says that
not only does the reduction of both metals from a mixture of
their carbonates with carbon work easier than sodium carbonate
alone with carbon, but even caustic soda may be used with
potassium carbonate and carbon. Also, the melting point of
potassium and sodium alloyed is much lower than that of either
one alone, in consequence of which their boiling point and the
temperature required for reduction are lower.
J. B. Thompson and W. WhiteJ specify mixing dry sodium
carbonate with a liquid carbonaceous material, preferably tar,
driving off all volatile matter in iron pots at a low heat, and
then distilling in a tubular fire-clay retort connected with a
tightly-closed receiver containing a little paraffin oil to ensure a
non-oxiding atmosphere, and also provided with a small escape
pipe for carbonic oxide. This process gave great prospects of
success when tried in the laboratory, but on a manufacturing
scale it failed for the reason (assigned by Mr. Thompson) that
the sheet-iron tray, designed to keep the material from attack-
ing the retort, absorbed carbon at about 1000° C. and fused,
after which no sodium was produced, since the material took
* Handbuch der Angewandten Chemie, 1830, ii. 345.
t Dingier, 143, 343- J English Patent 8426, June 11, 1887.
THE MANUFACTURE OF SODIUM. 203
up silica from the retort, absorbing so much that the carbon no
longer decomposed it.
H. S. Blackmore,* of Mount Vernon, U. S. A., patents the
following process of obtaining sodium: —
Calcium hydrate 273^ parts.
B erric oxide 31 "
Dry sodium carbonate 31 "
Charcoal loj!^ "
are intimately mixed and subjected to a red heat for 20 min-
utes, afterwards to a white heat. Caustic soda is first produced,
the carbon reduces the ferric oxide, producing iron, which in
its turn reduces the caustic soda, and sodium vapors distil.
The residue consists of ferric oxide and lime, and is slaked and
used over.
O. M. Thowlessf of Newark, N. J., claims to place a retort in
a furnace, providing it on one side with an arm through which
carboniferous material can be supplied, on the other side with a
similar arm (surrounded by flues), into which caustic soda or
sodium carbonate is charged — a valve controlling their flow into
the retort. Outside the furnace and on top of it is a flat con-
denser into which the sodium vapor passes.
G. A. JarvisI patents the replacement of the iron tubes or
crucibles used in the manufacture of sodium, by fire-clay ap-
paratus lined with basic material, such as strongly burnt mag-
nesia with 10 per cent, of fluorspar.
Castner's Process (1886).
The first public announcement of this process was through
one of the New York daily journals,^ and as the tone of the
article is above that of the usual newspaper reports, and the
expectations contained in it were subsequently more than
realized, we cannot better introduce a description of this process
than by quoting the paragraph referred to : —
♦English Patent 15 156, Oct. 22, 1888. f English Patent 12486 (1887).
X English Patent 4842, March 31, 1888. § New York World, May 16, 1886.
204 ALUMINIUM.
"When sodium was reduced in cost to $1.50 per lb. it was
thought to have touched a bottom figure, and all hope of mak-
ing it any cheaper seemed fruitless. This cheapening was not
brought about by any improved or new process of reduction,
but was owing simply to the fact that the aluminium industry
required sodium, and by making it in large quantities its cost
does not exceed the above-mentioned price. The retail price
is now $4.00 per lb. The process now used was invented by
Briinner, in 1808, and up to the present time nothing new or
original has been patented except three or four modifications of
his process which have been adopted to meet the requirements
of using it on a large scale. Mr. H. Y. Castner, whose labora-
tory is at 218 West Twentieth Street, New York, has the first
patent ever granted on this subject in the United States, and
the only one taken out in the world since 1808. Owing to
negotiations being carried on, Mr. Castner having filed appli-
cations for patents in various foreign countries, but not having
the patents granted there yet, we are not at liberty to state his
process fully. The metal is reduced and distilled in large iron
crucibles, which are raised automatically through apertures in
the bottom of the furnace, where they remain until the reduc-
tion is completed and the sodium distilled. Then the crucible
is lowered, a new one containing a fresh charge is substituted
and raised into the furnace, while the one just used is cleaned
and made ready for use again. The temperature required is
very moderate, the sodium distillling as easy as zinc does when
being reduced. Whereas by previous processes only one-third
of the sodium in the charge is obtained, Mr. Castner gets
nearly all, for the pots are nearly entirely empty when with-
drawn from the furnace. Thus the great items of saving are
two or three times as much metal extracted from a given
amount of salt, and cheap cast iron crucibles used instead of
expensive wrought-iron retorts. Mr. Castner expects to pro-
duce sodium at 25 cents per lb., thus solving the problem of
cheap aluminium, and with it magnesium, silicon, and boron,
all of which depend on sodium for their manufacture. Thus
THE MANUFACTURE OF SODIUM. 205
the production of cheap sodium means much more than cheap
aluminium. Mr. Castner is well known in New York as a
chemist of good standing, and has associated with him Mr. J.
H. Booth and Mr. Henry Booth, both well known as gentlemen
of means and integrity."
The following are the claims which Mr. Castner makes in
his patent:*
1. In a process for manufacturing potassium or sodium, per-
forming the reduction by diffusing carbon in a body of alkali
in a state of fusion at moderate temperatures.
2. Performing the reduction by means of the carbide of. a
metal or its equivalent.
3. Mechanically combining a metal and carbon to increase
the weight of the reducing material, and then mixing this pro-
duct with the alkali and fusing the latter, whereby the reducing
material is held in suspension throughout the mass of fused
alkali.
4. Performing the deoxidation by the carbide of a metal or
its equivalent.
For an explanation of the principles made use of in the
above outlined process we will quote from a lecture delivered
by Mr. Castner at the Franklin Institute, Philadelphia, October
1 2th, 1886. That Institution has since bestowed on Mr. Cast-
ner one of its gold medals as a recognition of the benefit to
science accruing from his invention.
" In the ordinary sodium process, lime is added to the reduc-
ing mixture to make the mass refractory, otherwise the alkali
would fuse when the charge is highly heated, and separate from
the light, infusible carbon. The carbon must be in the propor-
tion to the sodium carbonate as four is to nine, as is found
needful in practice, so as to assure each particle of soda in the
refractory charge having an excess of carbon directly adjacent
or in actual contact. Notwithstanding the well-known fact that
sodium is reduced from its oxide at a degree of heat but slightly
exceeding the reducing point of zinc oxide, the heat necessary
* U. S. Pat. No. 342,897, June i, 1886. Hamilton Y. Castner, New York,
206 ALUMINIUM.
to accomplish reduction by this process and to obtain even
one-third of the metal in the chai-ge, closely approaches the
melting point of wrought-iron.
" In my process, the reducing substance, owing to its com-
position and gravity, remains below the surface of the molten
salt, and is, therefore, in direct contact with fused alkali.
The metallic coke of iron and carbon contains about 30 per
cent, carbon and 70 per cent, iron, equivalent to the formula
FeCj. I prefer to use caustic soda, on account of its fusibility,
and mix with it such quantity of so-called ' carbide ' that the
carbon contained in the mixture shall not be in excess of the
amount theoretically required by the following reaction: —
3NaOHf FeC,=--3Na4-Fe + CO f CO.+sH ;
or, to every 100 lbs. of pure caustic soda, 75 lbs. of 'carbide,'
containing about 22 lbs. of carbon.
" The necessary cover for the crucible is fixed stationary in
each chamber, and from this cover a tube projects into the con-
denser outside the furnace. The edges of the cover are convex,
those of the crucible concave, so that when the crucible is raised
into position and held there, the tight joint thus made prevents
all leaking of gas or vapor. Gas is used as fuel, and the re-
duction begins towards 1000° C. As the dharge is fused, the
alkali and reducing material are in direct contact, and this fact,
together with the aid rendered the carbon by the fine iron, in
withdrawing oxygen from the soda, explains why the reduction is
accomplished at a moderate temperature. Furthermore, by
reducing from a fused mass, in which the reducing agent re-
mains in suspension, the operation can be carried on in crucibles
of large diameter, the reduction taking place at the edges of the
mass, where the heat is greatest, the charge flowing thereto from
the centre to take the place of that reduced.
" I am enabled to obtain fully 90 per cent, of the metal in the
charge, instead of 30 per cent, as formerly. The crucibles,
after treatment, contain a little carbonate of soda, and all the
iron of the 'carbide' still in a fine state of division, together
THE MANUFACTURE OF SODIUM. 207
with a small percentage of carbon. These residues are treated
with warm water, the solution evaporated to recover the car-
bonate of soda, while the fine iron is dried, and used over again
for 'carbide.' "
Mr. Castner having demonstrated in his New York laboratory
the success of his process, went to England, and for several
months during the winter of 1886-7 was engaged in building
and working a large sodium furnace. This was successfully car-
ried out near London, the inventor being assisted by Mr. J.
MacTear, F. C. S., who, in March, 1887, read a description of
this furnace and the results obtained before the Society of
Chemical Industry. During the working of this furnace it was
inspected by many chemical and metallurgical authorities, who
were completely satisfied as to its success. As the furnace
then described differed in a few details from the one just re-
ferred to, it may be well to extract the essential particulars from
Mr. MacTear's paper — on the ground that the importance of
this invention justifies a complete discussion of its develop-
ment:—
" Since Mr. Castner's paper upon his process, which was
read before the Franklin Institute of Philadelphia, October 12,
1886, several slight changes in the mode of carrying on this
process have been made. These have been brought about by
the experience gained from the actual working of the process
upon a commercially large scale.
"The reactions by which the sodium is produced are some-
what difficult to describe, as they vary somewhat according to
the mixture of materials and temperature employed in the re-
duction. The mixture and temperature which it is now pre-
ferred to use is represented by the reaction : —
6NaH0 + FeC2= 2Na2CO, + 6H + Fe + zNa.
" In place of using an actual chemical compound of iron and
carbon, as expressed by the above reaction, a substitute or
equivalent is prepared as follows : To a given quantity of melted
pitch is added a definite proportion of iron in a fine state of
208 ALUMINIUM.
division. The mixture is cooled, broken up into lumps, and
cooked in large crucibles, giving a metallic coke consisting of
carbon and iron, the proportions of each depending upon the
relative quantities of pitch and iron used. This metallic coke,
after being finely ground, provides a substance having the iron
and carbon in a like proportion to an iron carbide, and from
which neither the iron nor carbon can be separated by mechan-
ical means. The fine iron is conveniently prepared by passing
carbonic oxide and hydrogen in a heated state, as obtained
from an ordinary gas producer, over a mass of oxide of iron
commercially known as 'purple ore,' heated to a temperature
of about 500° C.
" In producing sodium, caustic soda of the highest obtain-
able strength is used, and there is mixed with it a weighed
quantity of the so-called ' carbide,' sufficient to furnish the
proper amount of carbon to carry out the reaction indicated
above. The crucibles in which this mixture is treated are made
of cast-steel, and are capable of containing a charge of 15 lbs.
of caustic soda, together with the proper proportion of the
• carbide.'
"After charging a crucible with the above mixture, it is
placed in a small furnace where it is kept at a low heat for
about thirty minutes, during which time the mass fuses, boils
violently, and a large part of the hydrogen is expelled by the
combined action of the iron and carbon, the ' carbide,' owing
to its gravity, remaining in suspension throughout the fused
soda. At the end of the time stated, the contents of the cru-
cible have subsided to a quiet fusion. The crucible is then
lifted by a pair of tongs on wheels and placed upon the plat-
form of the elevating gear, as shown in the drawing, (Fig. 18)
and raised to its position in the heating chamber of the main dis-
tilling furnace. The cover which remains stationary in the fur-
nace has a convex edge, while the crucible has a groove round the
edge into which the edge of the cover fits. A little powdered
lime is placed in the crucible groove just before it is raised, so
that when the edges of the cover and crucible come together
THE MANUFACTURE OF SODIUM.
209
they form a tight joint, and at the same time will allow the
crucible to be lowered easily from the chamber when the ope-
ration is finished, to give place to another containing a fresh
charge. From the cover projects a slanting tube (see Fig. 18),
connected with the condenser. The condenser is provided
with a small opening at the further end to allow the escape of
hydrogen, and has also a rod fixed (as shown), by means of
which any obstruction which may form in the tube during dis-
FlG. 18.
tillation may be removed. After raising a crucible in its place
in the furnace, the hydrogen escaping from the condenser is
lighted, and serves to show by the size of the flame how the
operation is progressing in the crucible, the sodium actually
distilling soon after the crucible is in its place. The temper-
ature of the reduction and distillation has been found to be
about 823° C. The gas coming off during the first part of the
distillation has been analyzed and found to consist of pure
hydrogen. Analysis of the gas disengaged when the ope-
14
2IO ALUMINIUM.
ration was almost completed, gave as a result, hydrogen 95 per
cent., carbonic oxide 5 per cent. It has been found advisable
to use a little more 'carbide' than the reaction absolutely re-
quires, and this accounts for the presence of the small quantity
of carbonic oxide in the expelled gas, the free carbon acting
upon the carbonate formed by the reaction, thus giving off car-
bonic oxide and leaving a very small percentage of the residue
in the form of peroxide of sodium. This small amount of car-
bonic oxide rarely combines with any of the sodium in the
tube, and so the metal obtained in the condensers is pure, and
the tubes never become choked with the black compound. In
the preparation of potassium a little less ' carbide' is used than
the reaction requires ; thus no carbonic oxide is given off, and
all danger attached to the making of potassium is removed.
After the reduction and distillation the crucible is lowered from
the furnace and the contents poured out, leaving the crucible
ready to be recharged. The average analyses of the residues
show their composition to be as follows: —
Carbonate of soda 77 per cent.
Peroxide of sodium 2 "
Carbon 2 "
Iron 19 "
" The average weight of these residues from operating upon
charges of 15 lbs. caustic soda and 5^ lbs. of carbide is 16
lbs. These residues are treated either to produce pure crystal
lized carbonate of soda or caustic soda, and the iron is recov-
ered and used again with pitch in the formation of the ' car-
bide.' From this residue weighing 16 lbs., is obtained 13 lbs.
of anhydrous carbonate of soda, equivalent to 9.4 lbs. caustic
soda of 76 per cent.
" Operating upon charges as above mentioned the yield- has
been —
Sodium, actual 2.50 lbs. Theory 2.85 lbs.
Soda carbonate, actual 13.00 lbs. " 13.25 lbs.
" The average time of distillation in the large furnace has
THE MANUFACTURE OF SODIUM. 2 1 I
been i hour 30 minutes, and as the furnace is arranged for
three crucibles, 45 lbs. of caustic soda are treated every 90
minutes, producing 7^ lbs. of sodium and 39 lbs. of carbonate
of soda. The furnace is capable of treating 720 lbs. of caustic
soda daily, giving a yield in 24 hours of 120 lbs. of sodium and
624 lbs. of anhydrous carbonate of soda. The furnace is heated
by gas which is supplied by a Wilson Gas Producer, consuming
I cwt. of fuel per hour. The small furnace in which the
crucibles are first heated requires about J^ cwt. per hour. The
following estimate of cost, etc., is given from the actual running
of the furnace working with the above charges for 24 hours : —
£ ^. d.
720 lbs. of caustic soda @ ;^i i per ton 3 10 10
1 50 lbs. of " carbide " @ yd^d. per lb o 6 4
Labor I o o
Fuel o 17 o
Re-converting 624 lbs. of carbonate into caustic, at a cost
of about £^ per ton on the caustic produced, say ... I o o
Total 6 14 2
Deducting value of 475 lbs. of caustic recovered 2 6 8
Cost of 120 lbs. of sodium ^4 7 6
Cost per pound, 83^</.
" Regarding the item of cost relating to the damage caused
to the crucibles by the heat, this question has been very care-
fully gone into, some of the crucibles have been used upwards
of fifty times, and from present indications of their condition
there is no doubt that they can continue to be used at least 150
times more before they become unfit for further use. In con-
sidering 200 operations to be the life of a crucible, the item of
damage or wear and tear amounts to less than \d. per lb. on
the sodium produced; and if we take the furnace tear and wear
at the same rate of \d. per lb., we will see that the tear and
wear of plant is only one-twelfth of that incurred in the ordi-
nary propess. It is upon these facts that Mr. Castner bases
his claim to be able to produce sodium by Jiis- process upon
the large scale, at a cost of less than 15. per lb. The advan-
212 ALUMINIUM.
tages of this process will be apparent to any one at all familiar
with the manufacture of these metals as conducted heretofore.
The first and most important end gained is their cheap produc-
tion, and this is owing chiefly to the low heat at which the
metals are produced, the quickness of the operation, non- clog-
ging of the conveying tubes, and a very small waste of mate-
rials. The process furthermore admits of being carried on
upon a very large scale ; in fact, it is intended ultimately to in-
crease the size of the crucible so as to make the charges con-
sist of 50 lbs. of caustic soda. Crucibles of cast iron have
been found quite suitable, and it is intended in future, to use
crucibles made of this material in place of the more expensive
steel."
Immediately on the demonstration of this success, a company
was formed to unite Mr. Castner's sodium process with Mr.
Webster's improvements in the production of aluminium chlor-
ide. The Aluminium Co., Ltd., first appeared before the public
in June, 1887, and at the first meeting in the following Septem-
ber it was decided to build works at once. These were begun
at Oldbury, near Birmingham, and were in working operation
by the end of July, 1888. The furnaces here erected were
larger than the one just described, and altogether had a pro-
ducing capacity of nearly a ton of sodium a day. The follow-
ing details respecting this plant and its working are taken
mostly from an address delivered before the Society of Arts,
March 13, 1889, by Mr. William Anderson, and from a dis-
course at the Royal Institution, May 3, 1889, by Sir Henry
Roscoe, president of the company.
There are four large sodium furnaces, each holding five pots
or crucibles, and heated by gas, applied on the regenerative
principle. A platform about five feet above the floor allows
the workmen to attend to the condensers, while the lifts on
which the pots are placed sink level with the floor. The
crucibles used are egg-shaped, about 18 inches diameter at
their widest part and 24 inches high ; when joined to the cover
the whole apparatus is about 3 feet in height. The covers
THE MANUFACTURE OF SODIUM. 213
have vertical pipes passing through the top of the furnace,
forming a passage for the introduction of part of the charge,
and also a lateral pipe connecting with the condenser. The
whole cover is fixed immovably to the roof of the furnace and
is protected by brickwork from extreme heat ; but it can easily
be removed when necessary. The natural expansion of the
vessels is accommodated by the water pressure in the hydraulic
lifts on which the pots stand. When the lift is lowered and
sinks with the lower part of the crucible to the floor level, a
large pair of tongs mounted on wheels is run up, and catching
Fig. 19,
A CASTNER SODIUM FURNACE.
hold of the crucible by two projections on its sides, it is carried
away by two men to the dumping pits, on the edge of which it
is turned on its side, the liquid carbonate of soda and finely-
divided iron which form the residue are turned out, and the
inside is scraped clean from the opposite side of the pit, under
the protection of iron .shields. When clean inside and out, it
is lifted again by the truck and carried back to the furnace, re-
ceiving a fresh charge on its way. It is then put on the plat-
form and lifted into place, having still retained a good red heat.
It takes only i)^ to 2 minutes to remove and empty a crucible.
214 ALUMINIUM.
and only 6 to 8 minutes to draw, empty, recharge, and replace
the five crucibles in each furnace. The time occupied in re-
ducing a charge is one hour and ten minutes. It is thus seen
that one bank of crucibles yields 500 pounds of sodium in
twenty- four hours, the battery of four furnaces producing about
a ton in that time.
The shape of the condenser has been altogether changed.
Instead of the flat form used on the furnace at London (see
Fig. 18), which resembled the condenser used in the Deville
process, a peculiar pattern is used which is quite different. It
consists in a tube-shaped cast-iron vessel S inches in diameter,
nearly 3 feet long over all, and having a slight bend upwards at
a point about 20 inches from the end. At this bend is a small
opening in the bottom, which can be kept closed by a rod drop-
ping into it; this rod, passing through a tight- fitting hole
above, can be raised or lowered from outside. Thus the
sodium can either run out continually into small pots placed
beneath the opening or can be allowed to collect in the con-
denser until several pounds are present, then a small potful run
out at once, by simply lifting the iron rod. The outer end of
the condenser is provided with a lid, hinged above, which can
be thrown back out of the way when required. This lid also
contains a small peep-hole covered with mica. In the top of
the condenser just before the end is a small hole through
which the hydrogen aud carbonic oxide gases escape when the
end is closed, burning with the yellow sodium flame. The
bend in the condenser is not acute enough to prevent a bar be-
ing thrust through the end right into the outlet tube projecting
from the furnace, thus allowing the whole passage to be cleaned
out should it become choked up. Previous to drawing the
crucibles from the furnace for the purpose of emptying them
and recharging, the small pots containing the metal distilled
from one charge are removed and empty ones put in their
place. Those removed each contain on an average about 6 lbs.
of sodium, or 30 lbs. from the whole furnace. When sufficiently
cool, petroleum is poured on top of the metal in the pots, and
THE MANUFACTURE OF SODIUM. 21 S
they are -vvheeled on a truck to the sodium casting shop, where
the sodium is melted in large pots heated by oil baths and cast
either into large bars ready to be used for making aluminium
or into smaller sticks to be sold. The sodium is preserved
under an oil such as petroleum, which does not contain oxygen
in its composition, and the greatest, care is taken to protect it
from water.
Special care is taken to keep the temperature of the furnace
at about iOOO° C, and the gas and air-valves are carefully re-
gulated so as to maintain as even a temperature as possible.
The covers remain in the furnace from Sunday night to Satur-
day afternoon, and the crucibles are kept in use till worn out,
when new ones, previously heated red-hot, are substituted
without interrupting the general running of the furnace. These
bottom halves of the crucibles are the only part of the plant
liable to exceptional wear and tear, and their durability is found
to depend very much on the soundness of the casting, because
any pores or defects are rapidly eaten into and the pot de-
stroyed. The average duration of each crucible is now 750
lbs. of sodium, or 125 charges.
Apropos of the reaction involved in the reduction, it has
probably been observed that Mr. MacTear proposes a different
formula from that suggested by Mr. Castner. Mr. Weldon re-
marked that when a mixture of sodium carbonate and carbon
was heated the carbon did not directly reduce the soda, but at
a high temperature the mixture gives off vapors of oxide of
sodium (Na^O) part of which dissociates into free oxygen and
sodium vapor; as soon as this dissociation takes place the
carbon takes up the oxygen, forming carbonic oxide, and thus,
by preventing the recombination of the sodium and oxygen,
leaves free sodium vapors.
Dr. Kosman, speaking in " Stahl und Eisen," January, 1889,
on Castner's process, gives the following explanation of the re-
actions taking place : —
Ten kilos of caustic soda and 5 kilos of carbide (containing
1.5 kilos of carbon) give the following reaction:
2l6 ALUMINIUM.
4NaOH + FeCj = Na^COs + Fe + 4H + CO + 2Na,
and half the sodium in the mixture is obtained.
Ten kilos of caustic soda and 10 kilos of carbide (containing
3 kilos of carbon) give this reaction —
zNaOH + FeQ = NaCO + Fe + 2H + CO + Na,
and half the sodium in the mixture is again obtained.
If 20 kilos of caustic soda and 15 kilos of carbide are mixed,
both the above reactions take place ; but if the ignition is con-
tinued, the sodium carboxyd (NaCO) reacts on the sodium
carbonate according to the reaction —
Na^COs + NaCO = sNa + 2CO2,
and the entire reaction may be represented by
sNaOH + FeC^ = sNa + Fe + 3 H + CO -h CO,,
and all the sodium in the mixture is obtained.
This is the reaction first proposed by Mr. Castner (see p.
206), and the proportions indicated by it gave him the largest
return of sodium. Mr. MacTear, however, states that the re-
action which takes place is conditioned largely by the tempera-
ture, and that at 1000° C. it is probably to be represented by
6NaOH -I- FeCj = 2Na2C03 + 6H -F Fe + zNa,
which is essentially the same as that given by Sir Henry Ros-
coe in his discourse, viz : —
3NaOH + C = Na.CO, + 3H. + Na.
This reaction would require 18^ lbs. of carbide to 50 lbs. of
caustic soda, and since the sodium carbonate is easily converted
back into caustic by treatment with lime, the production of so
much carbonate is offset by the ease with which the reaction
takes place, and the added advantage that the gas evolved with
the sodium is solely hydrogen, thus allowing the reduction to
THE MANUFACTURE OF SODIUM. 217
proceed in an atmosphere of that gas, and reducing the pro-
duction of the usual deleterious sodium carbides to a minimum.
A further discussion of this subject will come up in consider-
ing Netto's process.
Netto's Process (1887).
Dr. Curt Netto, of Dresden, took out patents in several
Eurupean countries,* which were transferred to and operated
by the AlHance Aluminium Company, of London (see p. 31).
The process is continuous, and is based on the partial reduc-
tion of caustic soda by carbon. Dr. Netto observes that car-
bon will reduce caustic soda at first at a red heat, but a white
heat is necessary to finish the reduction, the explanation being
that the reaction is at first —
4NaOH + C = Na^COa-l- 2H, -t- CO + Na„
and that the carbonate is only reduced at a white heat. To
avoid any high temperature, the first reaction only is made use
of, the carbonate being removed and fresh caustic supplied
continuously, and without interrupting the operation or admit-
ting air into the retort in which the reduction takes place.
A vertical cast-iron retort, protected by fire-clay coating, is
surrounded by flues. The flame after heating the retort passes
under an iron pot in which the caustic soda is kept melted, and
situated just above the top of the retort. This pot has an out-
let tube controlled by a stop-cock, by which the caustic may
be discharged into a funnel with syphon-shaped stem fastened
into the top of the retort. There is also a syphon-shaped out-
let at the bottom of the retort, through which the molten so-
dium carbonate and bits of carbon pass. A hole with tight lid
in the upper cover is provided for charging charcoal. A tube
passes out just beneath the upper cover, connecting with a
large condenser of the shape used by Deville (see Fig. 20).
In operating, the retort is heated to bright redness, filled one-
third with best wood charcoal, and then . molten caustic soda
♦German patent (D. R. P.) 45105; English patent, October 26, 1887, No. 14602.
2l8
ALUMINIUM.
tapped from the melting-pot into the funnel, the feed being so
regulated that the funnel is kept full and the retort closed.
The lower opening is kept closed until enough sodium carbon-
ate has accumulated to lock the syphon passage air tight.
When after several hours' working the charcoal is almost all
used up, the supply of caustic soda is shut off for a time and
Fig. 20.
the retort recharged through the opening in the upper lid,
when the operation goes on as before. The sodium carbonate
produced is easily purified from carbon by solution. Since
sodium vapor at a high temperature is very corrosive, all rivets
and screw joints must be avoided in making the retort. On
this account, the outlet tubes should be cast in one piece with
the retort.
THE MANUFACTURE OF SODIUM. 219
Both Netto's process and Castner's were in use for a con-
siderable time ( 1 888-1 891), and produced sodium in large
quantities and cheaply. With the advent of the cheaper elec-
trolytic methods of producing aluminium, the sodium methods
were put to a sharp struggle for existence. The Alliance Alu-
minium Company, working the Netto process, soon gave up
the fight. The Aluminium Company, Limited, working Cast-
ner's process, were enabled to continue making aluminium for
some time longer by an invention of Mr. Castner's to produce
sodium electrolytically. This process is still being used, but
the sodium produced is used for various other purposes than
making aluminium, the extraordinary cheapness of the electro-
lytic processes rendering competition impossible.
Reduction of Sodium Compounds by Electricity.
The decomposition of fused sodium chloride by the electric
current seems to promise the economic production of sodium,
for not only is this metal formed, but chlorine is obtained as a
by-product, its value reducing very much the cost of the
operation.
P. JablochofF has devised the following apparatus for decom-
posing sodium or potassium chlorides.* (Fig 21.)
The arrangement is easily understood. The salt to be de-
composed is fed in by the funnel into the kettle heated by a fire
beneath. The positive pole evolves chlorine gas, and the
negative pole evolves vapor of the metal, for, as the salt is
melted, the heat is sufficient to vaporize the metal liberated.
The gas escapes through one tube and the metallic vapor by
the other. The vapor is led into a condenser and solidified.
Prof. A. J. Rogers, of Milwaukee, Wis., has made a number
of attempts to reduce sodium compounds electrolytically, using
as a cathode a bath of molten lead and producing an alloy of
lead and sodium which he makes use of for the reduction of
aluminium compounds. Although these attempts are hardly
* Mierzinski.
220
ALUMINIUM.
past the experimental stage, yet the record of the results ob-
tained may very probably be interesting and valuable to other
investigators in this line.
Prof. Rogers reasons that from the known heat of combina-
FlG. 21.
unvrm |>T«"
tion of sodium and chlorine (4247 calories per kilo of sodium)
there is enough potential energy in a pound of coal to separate
nearly two pounds of sodium, if any mode of applying the com-
bustion of the coal to this end without loss could be devised.
If, however, this energy is converted into mechanical work, this
again into electrical energy, and this latter used to decompose
sodium chloride, we can easily compute the amount of coal to
be used in a steam boiler to produce a given amount of sodium
by electrolysis. Now, if the electric current could be applied
without loss in decomposing sodium chloride, i electric horse-
power (746 Watts) would produce about 8 lbs. of sodium in
24 hours. But as in practice one mechanical horse-power ap-
plied to a dynamo yields only 80 or 90 per cent, of an electric
horse-power, and as about 4 lbs. of coal are used per indicated
THE MANUFACTURE OF SODIUM. 221
horse-power per hour, from 105 to 120 lbs. of coal would be
required per day to produce this result, or about 15 lbs. per lb.
of sodium. Since, however, there is a transfer resistance in the
passage of the electric current through the molten electrolyte,
more than this will be required, in proportion to the amount of
current thus absorbed.
The temperature of fusion of sodium chloride is given by
Carnelly as Tj6° C, but Prof. Rogers remarks that the fusing
point may be lowered considerably by the presence of other
salts ; for instance, it melts about 200° lower if a small amount
of calcium chloride or potassium chloride is present. We will
quote the results of some experiments as given by Prof.
Rogers.*
"The following results were obtained among many others by
using a Grove battery, a Battersea crucible to hold the sodium
chloride, a carbon anode and an iron cathode terminating in a
tube of lime placed in the melted salt. As soon as metallic
sodium escaped and burnt at the surface of the liquid the cur-
rent was stopped. A little sodium was oxidized, but a consid-
erable amount was found in the tube in the metallic state. In
six experiments the amount of sodium obtained was from 50 to
85 per cent, of the theoretical amount, averaging 65 per cent.
It thus seemed that, with suitable apparatus, from 5 to 6 lbs. of
sodium could be obtained in 24 hours per electric horse-power.
Thus, if there were no practical difficulties in the construction
of the crucibles and other apparatus involved, nor in working
continuously on a large scale, the metal could be obtained at
small cost. Various forms of crucibles were used and attempts
made to distil the metal when formed at the negative electrode
(sodium volatilizing at about 900° C), but the sodium vapor
carries with it a large amount of sodium chloride as vapor, and
the distillation is attended with difficulty.
" During the last three years I have experimented on the
reduction of sodium chloride, using molten negative electrodes
and especially lead. Lead, tin, zinc, cadmium and antimony
* Proceedings of the Wisconsin Natural History Society, April, 1889.
222 ALUMINIUM.
all readily .alloy, with sodium, a large part of which can be re-
covered from the alloys by distillation in an iron crucible. They
can be heated to a higher temperature than pure sodium in
acid crucibles without the sodium attacking the crucible. In
the following experiments a dynamo machine was used to sup-
ply the current.
"Experiment i. A current averaging 72 amperes and 33
volts was passed through molten sodium chloride contained in
two crucibles arranged in series, for two hours. Each con-
tained 30 lbs. of salt; in the first was put 104 grammes of tin,
in the second 470 grammes of lead, each serving as cathode,
and connection being made through the bottom of the crucible.
A carbon anode passed through the cover and extended to
within three inches of the molten cathode. The crucible con-
taining the tin was nearer the fire and consequently hotter, and
had an average potential across the electrodes of 12 volts,
while that containing the lead cathode was 21 volts. When at
the end of two hours the carbons were removed and the cru-
cibles cooled and broken open, the lead alloy was found to
contain 96 grammes of sodium, or 17 per cent. There was
about 90 grammes of sodium found in the tin alloy, or between
45 and 50 per cent. Both these alloys rapidly oxidized in the
air, and when thrown into water the action was very energetic,
in the case of the tin alloy the liberated hydrogen being ignited,
and after the reaction the metals were found at the bottom of
the vessel in a finely divided state. Both these alloys reduce
cryolite or aluminium chloride."
In Prof. Rogers' further experiments cryoHte was added to
the bath, so that sodium was produced and aluminium formed
in one operation. (See under "Electrolytic Processes,"
Chap. XI.)
L. Grabau, of the " Aluminium Werke zu Trotha," has
made the following observations on the electrolysis of molten
sodium chloride. When the melted, salt is subjected to the
electric current, the resistance of the bath quickly rises and it
becomes almost inipossible to force the current through, This
THE MANUFACTURE OF SODIUM. 223
is probably due to the formation of a non-conducting sub-
chloride. The formation of this salt can be prevented by the
addition of some potassium chloride and the chloride of an
alkaHne-earth metal to the bath. In his patents,* Grabau
recommends the use of a mixture of sodium, potassium and
strontium chlorides, in the proportion of 88 sodium chloride,
112 potassium chloride, and 159 strontium chloride. With this
mixture, Grabau claims to obtain almost pure sodium, contain-
ing only about 3 per cent, of potassium and no trace of
strontium, while at the same time 95 per cent, of the metal
which the current should theoretically give is obtained. For
all the purposes to which sodium is now applied the presence of
the potassium is not in the least prejudicial. Borchers sub-
stantiates the fact that from a mixture of potassium and sodium
chlorides, which is very fluid, only sodium is liberated by the
current if it is not too strong and if the sodium chloride de-
composed is at once replaced. For carrying on his process,
Grabau uses the apparatus shown in Fig. 22. The positive
poles are carbon rods (C), the negative an iron pipe E, slit in
its lower part and surrounded by a bell-shaped porcelain cover
B. As the molten sodium is lighter than the bath material, it
rises into the pipe £ and passes away through the branch a into
a condenser where it collects under petroleum. The screw H
can be turned downwards to clean out the tube E in case it
stops up. It is intended that the vessel should be heated by
hot gases passing through the flues G G, and its temperature so
regulated that the sodium passes off in the liquid state. The
chlorine generated passes off by the tube d. In order to pre-
vent the corrosion of the cover B, Grabau has even con-
structed an apparatus in which it contained an iron lining and
was water-cooled.
The method now used by Castner .consists in electrolyzing
molten caustic soda at the lowest possible temperature. Pure
caustic soda melts below redness, and if kept at a temperature
♦German Patents (D. R. P.) Nos. 51898 and 56230 (1890).
224
ALUMINIUM.
not more than 20° above its melting point (310° C), it can be
easily and continuously electrolyzed. Arrangements must
therefore be provided for keeping the temperature of the bath
very constant, and for removing the sodium quickly from the
bath in order to prevent loss by corrosion. The apparatus
consists of an iron crucible, embedded in brickwork, in which
Fig. 22.
the caustic soda is melted by the heat of a circular gas burner
surrounding the pot (Fig. 23). The negative electrode passes
up through the bottom of the pot, the space between it and the
sides of the hole being allowed to fill up with solid caustic. A
tubular sleeve of iron descends from the cover and envelopes
the top of this electrode. Outside of this are the positive elec-
trodes. An opening is provided in the cover for the escape of
THE MANUFACTURE OF SODIUM.
225
gas and introduction of a thermometer. In operation, the heat
caused by the passage of the current is sufificient to keep the
bath melted. The free sodium floats on the surface of the bath
inside the iron sleeve surrounding the negative electrode, and
is skimmed off with a small ladle having fine perforations. The
operation is continuous, and afifords sodium at a cost probably
not greater than 15 cents per pound.
IS
CHAPTER VIII.
THE REDUCTION OF ALUMINIUM COMPOUNDS FROM THE
STANDPOINT OF THERMAL CHEMISTRY.
The branch of chemical science called thermal chemistry may
be said to be yet in its infancy. Although an immense mass
of thermal data has been accumulated, yet the era of great
generalizations in this subject has not yet been reached ; and
although we know with a fair degree of accuracy the heat of
combination of thousands of chemical compounds, including
nearly all the common ones, yet the proper way to use these
data in predicting the possibility of any proposed reaction re-
mains almost unknown. The principal barriers in the way are
two: 1st, the unknown quantities entering into almost every
chemical reaetion thermally considered, i. e., the heat of com-
bination of elementary atoms to form molecules of the ele-
ments ; 2d, the uncertainty as regards the critical temperature
at which a given exchange of atoms and consequent reaction
will take place. We will explain what is meant by these state-
ments.
To illustrate, let us consider the case of hydrogen uniting
with oxygen to form water according to the formula —
2(H— H) -I- (0= 0)= 2H,0
where (H — H) and (O ^ O) represent respectively molecules
of hydrogen and oxygen. Now, as i kilo of hydrogen unites
with 8 of oxygen to form 9 of water, setting free 34,462 units
of heat (calories), if we take the atomic weights in the above
reaction as representing kilos, we shall have the thermal value
of the reaction 4 X 34,462 = -|- 137,848 calories. But this'
quantity is evidently the algebraic sum of the heat evolved in
(226)
REDUCTION OF ALUMINIUM COMPOUNDS. 22/
the union of 4 kilos of hydrogen atoms with 32 kilos of oxygen
atoms, and the heat absorbed in decomposing 4 kilos of hydro-
gen gas into atoms! and 32 kilos of oxygen gas into atoms.
These two latter quantities are unknown, though a few chem-
ists have concluded from studies on this question that they are
probably very large. It has been calculated that the reaction
H -|- H = (H — H) sets free 240,000 calories,
and 0 4-0^ (O = O) sets free 147,200 calories ;
If these numbers are approximately true, then
4H + 20^ 2H2O would set free about 773,000 calories.
If these quantities are really anything like so large, and if
they are at sometime determined with precision, thermo-chem-
ical principles and conclusions will be greatly modified. Mean-
while, predictions based on the data we have, lose all possibility
of certainty, and so we need to keep in mind in our further
discussion that our deductions at the best are only probabil-
ities. Further, suppose that we mix i kilo of hydrogen gas
and 8 kilos of oxygen gas, put them in a tight vessel and keep
them at the ordinary temperature. No reaction will take place
in any length of time, even though 34,462 calories would be
set free thereby. The explanation of this is that the atoms of
hydrogen and oxygen are so firmly bound to each other in the
molecules, that the dissimilar atoms have not strength of afiSnity
sufiScient to break away in order to combine. It is well known
that a spark only is necessary to cause an explosive combina-
tion of the gases under the above conditions, the temperature
of the spark expanding the gases coming in contact with it,
causing the atoms to swing with more freedom in the molecules ;
and as soon as two atoms of hydrogen come within the .sphere
of attraction of an atom of oxygen and form a molecule of
water, the heat liberated is immediately communicated to the
adjacent atoms, and almost instantaneously the entire gases
have combined. The same principle undoubtedly holds true
228 ALUMINIUM.
in cases of reduction. Carbon may be mixed with litharge
and the mixture left in the cold forever without reacting, but at
a certain temperature the carbon will abstract the oxygen. The
temperatures at which reactions of this nature will take place
are often determined experimentally.
There are other points which are somewhat indeterminate in
these discussions, such as the influence of the relative masses
of the reacting bodies, their physical states, i. e., solid, liquid
or gaseous, also the influence of the physical conditions favor-
ing the formation of a certain compound ; but the nature of the
subject and the meagreness of data in the particular pheno-
menon of reduction, render it inexpedient if not impracticable
to take these points into consideration.
Starting with the above remarks in view, we will consider the
heat generated by the combination of aluminium with certain
other elements, as has been determined experimentally, and
study, from a comparison with the corresponding thermal data
for other elements, what possibilities are shown for reducing
these aluminium compounds.
The heat generated by the combination of aluminium with
the different elements is given as follows : the first column giv-
ing the heat developed by 54 kilos of aluminium (representing
AI2), and the second the heat per atomic weight of the other
element, e. g., per 16 kilos of oxygen.
Element. Compound. Calories. Calorie.s. Authority.
Oxygen * Al^Oj 391,600 130,500 Berthelot.
392,600 130,900 Bailie & F^ry.
Fluorine 2AIF3 552,000 92,000 Berthelot.
Chlorine 2AICI3 321,960 53,66o Thomsen.
Bromine 2AlBr3 239,440 39,900 "
Iodine 2AU3 140,780 23,460 "
Sulphur AI2S3 124,400 41,467 Sabatier.
* Berthelot's number represented the formation of the hydrated oxide, AIJO3.3H2O,
and, for want of knowing the heat of hydration, has been generally used as the heat
of formation of AljOj. Recently, J. B. Bailie and C. F4ry (Ann. de Chim. et de
Phys., June, 1889, p. 250) have, by oxidizing aluminium amalgam, obtained the above
figure for the heat of formation of AI2O3, and determined that the beat of hydration
is 3000 calories, which would make the heat of formation of the hydrated oxide
395,600.
REDUCTION OF ALUMINIUM COMPOUNDS. 229
Let US consider the theoretical aspect of the reduction of
alumina. The heat given out by other elements or com-
pounds which unite energetically with oxygen is as follows, the
quantity given being that developed by combination with 16
kilos (representing one atomic weight) of oxygen.
Element. Compound. Calories.
AlTiminlum AljOj 130,500
Sodium Na.p 99, 760
Potassium Kfi 100,000 ( ?)
Barium BaO 124,240
Strontium SrO 1 28,440
Calcium CaO 130,930
Magnesium MgO 145,860
Manganese MnO 95,ooo ( ?)
Silicon SiOj 1 10,000
Zinc ZnO 85,430
Iron FejOj 63,700
Lead PbO 50,300
Copper CuO 37>i6o
" CU2O 40,810
Sulphur SO2 35.540
Hydrogen H^O 68,360
Carbon CO 29,000
" COj 48,480
Carbonic anhydride CO^ 67,960
Potassium cyanide KCyO 72,000
On inspecting this list we find magnesium to be the only metal
surpassing aluminium, while calcium is about the same. This
would indicate that the reaction
AlA + 3Mg = Al, + 3MgO
would, if it were possible to bring the alumina and magnesium
in the proper conditions for reacting, develop about
(145,860 — 130,500) X 3 = 46,080 calories,
and points to the possibility of reducing alumina by nascent,
molten, or vaporized magnesium, under certain conditions. In
fact, since this paragraph was first written, in 1890, Dr. Clemens
Winkler has succeeded in performing the reduction in part.*
* Berliner Berichte, 1890, p. 772.
230 ALUMINIUM.
He found that when alumina was heated with magnesium pow-
der in a current of hydrogen, a nearly black powder resulted,
containing a lower oxide of aluminium, AlO, the reaction
being
2AI2O, + Mg = MgO.AljO, + 2AIO ;
the magnesia formed uniting with alumina to form an alum-
inate.
We notice further the fact that sodium or potassium could
not reduce alumina without heat being absorbed in large
quantity, and it is interesting to remember that some of the
first attempts at isolating aluminium by using potassium were
made on alumina, and were unsuccessful, so that it is practi-
cally acknowledged that while these metals easily reduce other
aluminium compounds (according to reactions which are ther-
mally possible, as we shall see later on) yet they cannot reduce
alumina, under any conditions so far tried.
When we consider the case of reduction by the ordinary re-
ducing agents, hydrogen, carbon, or potassium cyanide, we are
confronted in every case with large negative quantities of heat,
i. e., deficits of heat. So large do these quantities appear that
it is very small wonder that the impossibility of these reduc-
tions occurring under any conditions has been strongly affirmed,
For instance
Al203-f-6H=AU-|-3H,0
would require
(130,500 — 68,360) X 3 = 186,420 calories.
AI2O3 + 3C =Alj -I-3CO 304,500 calories.
AI2O3 + i>^C = AI2 -h ii^COa 246,060 calories.
Al,03 -I- 3KCy = Al, + 3KCyO 175,500 calories.
AlA +3CO =h\ + 7,C0, 187,620 calories.
The above quantities represent the differences between the
heats of formation of alumina and the product of the reduc-
tion, assuming the reaction to take place at ordinary temper-
atures. At high temperatures these heats of formation are in
REDUCTION OF ALUMINIUM COMPOUNDS. 23 1
general less than they would be at low heats, and if the heat of
formation of alumina decreases faster than .the heat of combi-
nation of the reducing agent with oxygen, the dififerences noted
above would be less and the reaction easier to produce. This
must be what actually takes place. For instance, at the heat
of an electric furnace, say 2500° to 3000°C., molten alumina
is reduced by carbon present in large quantity, that is, the dif-
ference beiween the heats of formation of AI2O3 and 3 CO has
become so small that the reaction takes place. Similarly,
Warren has recently reduced alumina by heating it in a lime
tube by an oxy-hydrogen blow-pipe, passing hydrogen through
the tube. We here have a reaction which is negative by 186,-
000 calories at ordinary temperatures, taking place at a tem-
perature probably not over 2000°C.
The conditions which render the carrying out of these diffi-
cult reductions possible are therefore :
1 . A high temperature, which weakens the heat of formation
of alumina.
2. An excess of the reducing agent, which is thus assisted
simply by the overpowering influence of its mass.
3. Fluidity of the substance to be reduced.
4. Intimate contact with the reducing agent.
5. Favorable conditions for the formation and removal of the
gaseous products of the reduction.
Concerning these, I would remark that the fluidity of the sub-
stance to be reduced may be attained by other means than a
high temperature. The alumina may, for instance, be liquefied
by solution in a bath of molten cryolite. If we dissolve it in
molten caustic soda we get a combination of alumina and soda
which will remain fluid if too much alumina is not added.
Such fluidity also allows much more intimate contact with the
reducing agent if it is a solid. . If the reducing agent is a gas,
most intimate contact is obtalined by finely pulverizing the alu-
mina. If the reducing agent is a solid and the product of the
reduction would be a gas, its formation would be accel-
erated by reducing the pressure in the apparatus. In other
232
ALUMINIUM.
words, a partial vacuum would undoubtedly aid in bringing
about the reduction, and would help to keep the aluminium in
the metallic state by removing quickly the product of reduction
and so preventing re-oxidation. I have no hesitation in affirm-
ing that since we now know that carbon does reduce molten
alumina below 3000°, and hydrogen reduces solid alumina at
2000°, the application of correct principles by intelligent inves-
tigators, with properly constructed apparatus, would undoubt-
edly result in discovering methods of producing the same reac-
tions at lower temperatures and on a larger scale. Whether
these methods of producing aluminium could compete with the
present electrolytic ones is another question, but it is certainly
interesting to mark the possibility of processes which some
future investigator may bring to commercial success.
As the basis of our discussion of the reduction of aluminium
chloride, bromide, or iodide, we give a table of heat developed
by the combination of some of the elements with one atomic
weight (in kilos) of each of these haloids.
Element.
Com-
pound.
Calories.
Com-
pound.
Calories.
Com-
pound.
53>66o
AlBrj
40,000
AII3
105,600
KBr
95.300
KI
97,690
NaBr
85,700
NaT
93.810
BaBr^
97.37°
SrBr^
85,000
92,270
CaBr^
78,900
84,910
70,400
75.5°°
56,000
f 5o,6oot
1 48,600*
jZnBr,
f43.ioot
] 40,640t
I 37.500*
[znP
41,380
PbBrj
32,200
Pblj
41.275
H&Br,
34.150
Hg,I,
40,400
41,000
FeBrj
24,000
Felj
32.87s
Cu^Br^
25,000
C%I,
22,000
HBt
8,400
HI
Calories.
Aluminium
Potassium . .
Sodium
Lithium ....
Barium ....
Strontium . .
Calcium ....
Magnesium.
Manganese .
Zinc
Lead
Mercury . . . •
Tin
Iron
Copper . . . .
Hydrogen. .
AlCl,
KCl
NaCl
LiCl
BaClj
SrClj
CaClj
MgCL,
MnCL,
ZnClj
PbCl^
Hg,Cl,
SnCL,
FeCl.,
CuoCl.^
HCl
23,460
80,100
69,000
f 30,coot
■j 26,600
(. 24,500
20,000
24,200
8,ooot
16,000
— 6,000
*Thomsen. t Andrews. J Jahresbericht der Chemie, 1878, p. 102,
On inspecting this table we notice that, in general, all the
REDUCTION OF ALUMINIUM COMPOUNDS. 233
metals down to zinc develop more heat in forming chlorides, and
very probably also in forming bromides and iodides, A re-
action, then, between aluminium chloride and any of these
metals, forming aluminium and a chloride of the metal, would
be exothermic, which means, generally speaking, that if alu-
minium chloride and any one of these metals were heated to-
gether to the critical point at which the reaction could begin,
the reaction would then proceed of itself, being continued by the
heat given out by the first portions which reacted. Zinc seems
to lie on the border line, and the evidence as to whether zinc
will practically reduce these aluminium compounds is still con-
tradictory, as may be seen by examining the paragraphs under
" Reduction by Zinc." (Chap. XII.)
Of the first six metals mentioned in the table after aluminium,
only potassium and sodium are practically available. The re-
action
AlCl3 + 3K = AH-3KCl develops 155,820 cal.
AlCls-F 3Na = Al-f- 3NaCl develops 132,090 cal.
and the result of this strong disengagement of heat is seen
when, on warming these ingredients together, the reaction once
commenced at a single spot all external heat can be cut off, and
the resulting fusion will become almost white hot with the heat
developed. In fact, the heat developed in the second reaction
would theoretically be sufficient to heat the aluminium and
sodium chloride produced to a temperature between 3000° and
4000°.
Magnesia should act in a similar manner, though not so vio-
lently, since
2AlCl3 + 3Mg=Al2 + 3MgCl2 develops 131,000 cal.
And manganese possibly also, since
2AICI3 + 3Mn = Ala -f- 3MnCl develops 14,040 cal.
The reduction of aluminium chloride, bromide, or iodide by
hydrogen is thermally strongly negative, which would indicate
a very small possibility of the conditions ever being arranged so
234 AXUMINIUM.
as to render the reaction possible. For instance, taking the
most probable case,
AICI3 + 3H = Al + 3HCI requires 94,980 calories.
The only probable substitutes for sodium in reducing alumin-
ium chloride are thus seen to be magnesium (whose cost will
probably be always greater than that of aluminium), manganese
(which may sometime be used in the form of ferro-manganese
for producing ferro-aluminium), and zinc (whose successful
application to this purpose would be a most promising advance
in the metallurgy of aluminium).
In 1886 Moissan isolated fluorine, and in 1889 he and Berthe-
lot measured the heat of formation of hydrofluoric acid. With
this datum, it became possible to calculate a table of the heat
of formation of the fluorides.* These can now be given as
follows, stating the heat evolved by combination with one
atomic weight (19 kilos) of fluorine.
Element. Compound, Heat evolved.
Potassium KF 1 10,000
Sodium NaF 109,700
Barium BaF^ 112,000
Strontium SrFj 112,000
Calcium CaF, 108,000
Magnesium MgFj 105,000
Aluminium AIF3 92,000
Manganese MnFj 72,000
Zinc ZnFg 69,000
Cadmium CdF^ 61,000
Iron FeF^ 63,000
Cobalt C0F2 60,000
Nickel NiFj 59,500
Copper CuFj 44,000
Silver AgF 25,500
Hydrogen HF (gas) 37,6oo
" " (in solution) 49,400
It follows from an inspection of these quantities that the
fluorides are stronger compounds than either the oxides, chlor-
ides, bromides or iodides. It is also seen that aluminium
* See a paper on this subject, by the author, in the Journal of the Franklin Insti-
tute, June, 1891.
REDUCTION OF ALUMINIUM COMPOUNDS. 235
stands in the same relative position as in the chlorides, except
that it is here stronger than manganese or zinc. It follows that
only sodium, potassium or magnesium of the available metals
wilU reduce aluminium fluoride. For such reductions the latter
must be liquefied by mixture with a fusible salt not acted on by
the reducing agent. Thus, we* would have
2AIF3 + 6Na= 6NaF+ 2AI, evolving 106,200 calories.
2A1F3 + 3Mg = 3MgF2 + 2AI, evolving 78,000 calories.
The reaction with zinc would absorb heat as follows :
2AIF3 + 2Zn= 2ZnF2 + 2 Al, absorbing 138,000 calories.
While the first two reactions take place easily, at a red heat,
the latter is nearly impracticable. The writer brought zinc into
contact with highly heated cryolite (AlFj.sNaF), and obtained
0.6 per cent, of aluminium in the zinc* The temperature was
a bright red, and this small amount of reduction shows that an
excess of zinc at a high temperature will to a small extent over-
come the affinity of aluminium for fluorine. Manganese in the
form of ferro-manganese, might take up even a larger percent-
age of aluminium than the above, yet no substantial amount of
reduction can be looked for from these elements.
In order to discuss the thermal relations of aluminium sul-
phide, we will make use of the following data, the heat devel-
oped being per atomic weight (32 kilos) of sulphur combining:
Element. Compound. Calories.
Alumlnitiin AI283 41,467
Potassium KjS 103,700
Sodium Na^S 88,200
Calcium CaS 92,000
Strontium SrS 99,200
Magnesium MgS 79,600
Manganese MnS 46,400
Zinc ZnS 41.326
Iron FeS 23,576
Copper Cu^S 20,270
Lead • PbS 20,430
Hydrogen HjS 4>740
Carbon CSj —14,500
* See details in Chapter XII.
236 ALUMINIUM.
These figures point to the easy reduction of aluminium sul-
phide by potassium, sOdium, or magnesium, and its possible
reduction by manganese and zinc. The other metals would
require exceptional conditions, perhaps, of temperature, for
their action. It is interesting to note that two observers have
determined from the deposition -of the metals from solution by
hydrogen sulphide, that the order of the afifiinity of the metals
for sulphur is first the alkaline metals, then the others in the
following order: copper, lead, zinc, iron, manganese, and then
aluminium and magnesium — with the remark that the affiinities
of the latter two for sulphur appear quite insignificant. The
explanation of this difference is that the metals last mentioned
form sulphides which are not stable in water, but are immedi-
ately decomposed according to the reaction
3 AI2S3 + 3 H2O = AI2O3 + 3H2S, evolving 77,840 calories,
while the alumina produced is immediately soluble in the weak
acid solution and at once disappears. It follows that these ele-
ments are not precipitated as easily from solution as those
whose sulphides are not thus decomposed by water.
The reduction of aluminium sulphide by copper, tin and iron
is in a measure possible when the operation is conducted at a
high temperature and there is an excess of reducing metal
present. Under these conditions, a part of the aluminium sul-
phide is reduced and an alloy formed, but such reactions can-
not approach in completeness those reactions which are
strongly endothermic. The reduction by hydrogen is seen to
be highly improbable, and by carbon still more so.
The question of reducing aluminium compounds by the use of
electricity is a very different question. Looked at as a reduc-
ing or decomposing agent, the electric current is almighty. A
current with a tension of i volt will decompose any fluoride,
chloride, bromide or iodide whose heat of combination with one
atom weight of fluorine is less than 23,000 calories ; at a tension
of two volts, any less than 46,000 calories ; and therefore at a
tension of five volts would decompose the strongest of any of
REDUCTION OF ALUMINIUM COMPOUNDS. 237
these salts. Such a current only means half a dozen ordinary
copper sulphate batteries connected in tension. For oxides
and sulphides, the heat of combination with one-half an atomic
weight must be used, which quantity is equal in combining
power to one whole atomic weight of the above elements, and
then the same rule applies. We can thus calculate the voltage
required to decompose the following anhydrous molten com-
pounds—
» Element. Fluoride. Chloride. Oxide. Sulphide.
Potassium 4.8 4.6 2.2 2.3
Sodium 4.7 4.3 2.2 1 .9
Barium 4.9 4.3 2.7 2.2
Strontium 4.9 4.0 2.75 2.2
Calcium 4.7 3.7 2.85 2.0
Magnesium 4.6 3.3 3.2 1.7
Aluminiuin 4.0 2.3 2.8 0.9
Manganese 3.1 2.4 2.1 l.o
Zinc 3.0 2.3 1 .9 0.9
Iron 2.7 1.8 1.5 0.5
Nickel 2.5 1.6 1.3 0.4
Copper 1.9 1.4 0.9 0.4
Silver i.i 1.3 o.l o.i
Hydrogen 1.6 i.o 1.5 0.1
A critical comparison of these figures leads to some very in-
teresting conclusions. We notice, in the first place, that in the
fluorides there is a very sharp drop after aluminium ; in these
salts aluminium has closer resemblance to the alkaline earth
fluorides, while manganese and zinc resemble the ordinary
metals. In the chlorides, there is a sharp drop before alumin-
ium, leaving it in stronger resemblance to the zinc, manganese
and lower metallic salts. In the oxides, aluminium is again
classed with the alkaline earth metals, and sharply separated
from the lower metallic oxides. Attention is particularly called
to the irregularity of the alkaline metals, whose oxides are as
easily decomposed as those of the metals below aluminium.
This explains why we can reduce these alkaline metals more
easily by carbon than we can alumina, and yet we can use the
alkaline metal to react on a salt of aluminium and get metallic
238 ALUMINIUM.
aluminium. The high voltage required to decompose mag-
nesium oxide also explains the wonderful efficiency of mag-
nesium as a reducing a:gent when acting on the oxides. In the
list of sulphides, we again notice a sharp drop before alumin-
ium, leaving it in close correspondance with manganese and
zinc. The very low voltage required is also noticeable ; a
single Daniell cell should be able to produce decomposition.
Take a bath, for instance, in which alumina is being decom-
posed using a tension of 5 volts, of which 2.8 is absorbed in
decomposition and 2.2 in overcoming other resistances. If
aluminium sulphide were the material decomposed, assuming
other resistances the same as before, the total resistance of the
bath would be overcome by 3.1 volts; or, in other words, it
would require only 62 per cent, of the power to produce the
same weight of aluminium. The sulphide thus presents great
advantage in respect to ease of decomposition.
Next to the sulphide, the chloride is the easiest to decom-
pose, but both these salts are difficult to produce, and herein
lies their chief disadvantage.
It can be furthermore observed, that if we mix these various
salts into one bath, and use an electric current carefully regu-
lated as to tension, we can act on pne ingredient without dis-
turbing to any extent the others present. We could, for
instance, mix aluminium chloride with any fluoride down to
that of zinc, and by a tension of 2.5 volts or a little over sepa-
rate out only alumininum. We could mix alumina with any
fluoride or chloride above aluminium in the list, and get only
aluminium from the bath. The fact is, however, that alumina
is not dissolved by the chlorides, but only by the fluorides.
These latter are therefore available, and are the principal salts
used at present in the aluminium industry. Thus, in Hall's
process we have present in the bath
Alumina requiring 2.8 volts for decomposition.
Aluminiunl fluoride " 4.0 " "
Sodium '■ " 4.7 . " , •'
When the current is passed through such a mixture, and its
REDUCTION OF ALUMINIUM COMPOUNDS. 239
tension does not rise abnormally high,' the bath being kept sat-
urated with all the aluimina it can dissolve, the only ingredient
decomposed is the alumina.
In Minet's process there are present :
Alumina, requiring 2.8 volts.
Aluminium fluoride, " 4.0 "
Sodium fluoride, " 4^7 "
Sodium chloride, " 4.3 "
The minimum electro-motive force required to decompose
this bath at 900° is 2.4 volts; at 1100°, 2.17 volts. The elec-
tro-motive force of carbon burning to carbonic oxide at those
temperatures is, however, 0.65 volts, so that the voltage re-
required to decompose liquid alumina at these temperatures is
0.65 volts higher than the figure given. We therefore have
these data for the decomposition of alumina :
Voltage for
Temperature.
Decomposition.
Heat of Formation.
0°
2.82
392,600 (solid aluminium.)
0°
2.78
387,200 (liquid aluminium).
900°
3-05
424,600 (liquid aluminium).
1100°
2.82
392,600 (liquid aluminium).
The equation for the voltage required to decompose alumina
producing liquid aluminium is therefore :
V^ 2.78 + 0.00129 t — 0.00000128 1'',
and the heat required to decompose the molecule of alumina is
Q = 387,200+ 192 t — 0.1766 1^
This formula is extremely interesting from a thermo-chemi-
cal point of view in enabling us to calculate theoretically the
temperature at which hydrogen or carbon begins to reduce alu-
mina. The heat of formation of gaseous water ,at zero is accu-
rately known, and the experiments of Mallard and Le Chatelier
on the specific heats of hydrogen, oxygen and water vapor
enable us to calculate the heat of formation at any desired tern-
240 ALUMINIUM.
perature. From these data we calculate the heat of formation
of 3HjO to be represented by the formula:
Q = 174,300+ 7.71 t — 0.0072 t\
Now to find the temperature at which hydrogen gas would be-
gin to reduce alumina, we equate this formula with the one
given for the heat of the formation of alumina, and have
387,200 + 192 t — 0.1766 t''= 174,300+ 7.71 t— 0.0072 t''
from which
t = i785°C.
This will be the temperature at which the heat of formation
of 3H2O will be exactly equal to the heat of formation of Al^Oj,
and consequently immediately above this temperature reduc-
tion will begin if the physical conditions are favorable for the
reaction taking place.
On a similar principle we can calculate the temperature at
which carbon will begin to reduce aluminium, except that the
operation is more difficult because of the variable specific heat
of carbon. I have calculated from Weber's results that the heat
in carbon from zero to high temperatures may be expressed as
Q = o.5 t — 120.
Taking this quantity, in connection with the specific heats of
oxygen and carbonic oxide as determined by Mallard and Le
Chatelier at high temperatures, we have for the heat of forma-
tion of 3CO at any temperature t above 1000°, the expression
Q = 83.35s + 8.6472 t - 0.0009 t^
For finding the temperature at which reduction begins we have
387,200 + 192 t — 0.1716 t'' = 83,355 + 8.6472 t — 0.0009 ^^
from which
t = 1980°.
REDUCTION OF ALUMINIUM COMPOUNDS. 24 1
The temperatures above calculated appear much lower than
has heretofore been deemed possible, but they are supported by
experimental evidence ; viz., the reduction of alumina by
hydrogen performed by Warren, at a temperature which it is
hardly possible could have been higher than 2000° ; and the
production of pig-iron containing over i per cent, of aluminium
in a Pennsylvania blast furnace. The highest temperature at-
tained in this furnace, not of very modern construction, could
not have exceed 2000° C. (For details, see Chapter XII.)
If in place of free hydrogen gas or free carbon we use as a
reducing agent a combination of these two which gives out heat
in its dissociation into carbon and hydrogen, we would have a
more efficient reducing agent than if the constituents were used
separately. Such a compound is Acetylene, CjHj, which ab-
sorbs heat in its formation and therefore gives out heat in its
decomposition. At ordinary temperatures, Berthelot has found
that
C2 + H2 = C.2H.2 absorbs 5 1,500 calories.
We do not know exactly how this number varies with the tem-
perature, as we lack the specific heat of CJ-Ij, but we know that
it does not change very much. We would therefore have the
reduction equation as follows —
AI2O3 + C.,H2 = 2AI + 2CO -I- H,0
and the heat requirements as follows —
Reducing AljOa ■• 387,200 -|- 192.61— 0.17161'' (l)
Developed in forming 2CO 55.57° -f- S-76t — o.ooo6t'' (2)
" " « HjO 58,000-1- 2.571— 0.00251^ C3>
" " decomposing CijHj. 51,500 (4)
If we put (i) = (2) + (3) + (4) and solve for t, we obtain
the theoretical temperature at which Acetylene should begin to
reduce alumina as
t=-i87o°C.
This temperature, it will be observed, is not so low as that
16
242 ALUMINIUM.
calculated for pure hydrogen. Six months ago, this calculation
would have been of purely scientific interest, because pure
acetylene was a difiScult substance to procure ; but a very prac-
tical interest has been given it by the recent invention of Mr.
Thomas L. Willson of Brooklyn*, whereby pure acetylene can
be manufactured at a cost approximating 2 cents per pound.
Since the gas should theoretically reduce double its weight of
aluminium, if perfectly utilized for reduction, the cost of the re-
ducing agent per pound of aluminium would be very small. It
is to be hoped that the possibility of the above reaction may be
tested with this powerful reducing agent.
Before closing this subject of the thermal aspect of the reduc-
tion of aluminium compounds, it may be interesting to notice
some of the reactions which are of use in the aluminium indus-
try. It is well known that while chlorine gas can be passed
over ignited alumina without forming aluminium chloride, and
while carbon can be in contact with alumina at a white heat
without reducing it, yet the concurrent action of chlorine and
carbon will change the alumina into its chloride, a compound
with a lower heat of formation. Thus —
AL^Os -f- 3C = AI2 4- 3CO requires 304,500 cal.
But AI2O3 + 3C + 6C1 = 2AICI2 + 3CO requires a quantity of
heat equal to the 304,500 cal. minus 321,960, the heat of for-
mation of aluminium chloride, or in other words, 17,360 cal. is
evolved, showing that the reaction is one of easy practicability.
If it be inquired whether there is not some chloride which
would act on alumina to convert it into chloride, we would re-
mark that if we can find a chloride whose heat of formation is
as much greater than the heat of formation of the correspond-
ing oxide as the heat of formation of aluminium chloride is
greater than that of alumina, then such a chloride might react.
* See description in Engineering and Mining Journal, Dec. 15, 1894.
REDUCTION OF ALUMINIUM COMPOUNDS. 243
To be more particular, to convert alumina into aluminium
chloride, a deficit of 391,600 — 321,960 = 69,640 calories must
be made up. If we know of an element which in uniting with
3 atom weights (48 kilos) of oxygen gives out 69,640 calories
more heat, or a still greater excess, than in uniting with 6 atom
weights (213 kilos) of chlorine, then the chloride of that ele-
ment might perform the reaction. Now —
6Na + 3O = sNajO evolves 299,280 cal.
and 6Na + 6C1 =6NaCl evolves 586,140 cal.
leaving evidently a balance of 286,860 calories in the opposite
direction to what we are looking for. And so for every metal
except aluminium, I find the heat of formation of its chloride
greater than an equivalent quantity of its oxide. The only
element which I know to possess the opposite property is
hydrogen, for —
6H + 3O — 3H2O evolves 205,080 cal.
and 6H + 6C1 = 6HC1 evolves 132,000 cal.
and therefore the reaction —
AI2O3 + 6HC1 = 2AICI3 + 3H2C
would evolve according to our calculations (205, 080 — 132,000) —
69,640=3,440 calories, and would be thermally considered a pos-
sible reaction. Moreover, as a secondary effect, the water formed
is immediately seized by the aluminium chloride, for the reaction
2AICI3 + 3H2O = 2AICI3.3H2O evolves 153,690 cal.
and thus increases the total heat developed in the decom-
position of the alumina to 158, [30 calories. The result of
this reaction is therefore the hydrated chloride, which is of no
value for reduction by sodium, since when heated it decom-
poses into alumina and hydrochloric acid again, that is, it will
decompose before giving up its water, and the water if unde-
composed, or the acid if it decomposes, simply unites with the
244 ALUMINIUM.
sodium without affecting the alumina. The immense heat of
hydration, 153,690 calories, is so much greater than any other
known substance, that it is vain that we seek for any material
which might abstract the water and leave anhydrous aluminium
chloride.
Analagous to the reaction by which aluminium chloride is
formed from alumina is the reaction made use of for obtaining
aluminium sulphide, yet with some thermal considerations of a
different and highly interesting kind. If a mixture of alumina
and carbon is ignited and, instead of chlorine, sulphur vapor is
passed over it, no aluminium sulphide will be formed. An ex-
planation of this fact is seen on discussing the proposed reac-
tion thermally.
AI2O3 + 3C -I- 3S = AI2S3 + 3CO requires 180,200 cal.
It will be remembered that the similar reaction with chlorine
evolved 17,360 calories; the quantity causing this difference is
the heat of combination of aluminium sulphide, which is 321,960
— 124,400 = 197,560 calories less than that of aluminium
chloride, changing the excess of 17,360 calories into a deficit of
180,200 calories. This large negative quantity shows a priori
that the reaction could be made to occur only under excep-
tional conditions, and its non-occurrence under all conditions
so far tried gives evidence of the utility of the study of thermo-
chemistry, at least as a guide to experiment. However, while
carbon and sulphur cannot convert alumina into aluminium sul-
phide, carbon bisulphide can, for a current of the latter led over
ignited alumina converts it into aluminium sulphide. The re-
action taking place is
Al^Oa + 3CS2 = A1,S3 + 3COS.
Now, since carbon and sulphur by themselves could not per-
form the reaction, we should be very apt to reason that a com-
pound of carbon and sulphur would be still less able to do so,
since the heat absorbed in dissociating the carbon-sulphur
REDUCTION OF ALUMINIUM COMPOUNDS. 245
compound would cause a still greater deficit of heat. But here
-is precisely the explanation of the paradox. Carbon bisulphide
is one of those compounds, not frequent, which has a negative
heat of formation ( — 29,000 calories), i. e., heat is absorbed in
large quantity in its formation, and therefore, per contra, heat
is given out in the same quantity in its decomposition. The
heat of formation of carbon oxysulphide being 37,030 calories,
we can easily compute the thermal value of the reaction just
given.
Ifeat absorbed.
Decomposition of alumina 391,600 cal.
Heat developed.
Decomposition of carbon bisulphide 87,000
Formation of carbon oxysulphide 1 1 1,090
" of aluminium sulphide 124,400
322,490 cal.
Deficit of heat 69,1 10 "
It is thus seen that the reaction with carbon bisulphide is
less than one-half as strongly negative as the reaction with car-
bon and sulphur alone, and we therefore have an explanation
of the fact that the reaction with carbon bisulphide is easily
practicable, while the other is not. We do not know enough
about the variation of the heats of formation of aluminium sul-
phide and carbon oxysulphide to be able to make calculations
as accurately as was possible with the question of reducing alu-
mina, but if all the heats of formation remained constant except
that of alumina, the 69,000 calories deficit would be made up
by the decrease in the heat of formation of chat substance at
975O C, which is somewhere about the temperature at which
the reaction really takes place.
CHAPTER IX.
REDUCTION OF ALUMINIUM COMPOUNDS BY MEANS OF
POTASSIUM OR SODIUM.
The methods comprised under this heading may be con-
veniently divided into two classes : —
I. Methods based on the reduction of aluminium chloride
or aluminium-sodium chloride.
II. Methods based on the reduction of cryolite or aluminium
fluoride.
I.
The methods here included can be most logically presented
by taking them in chronological order.
Oerstedt's Experiments (1824).
After Davy's unsuccessful attempts to isolate aluminium by
the battery, in 1807, the next chemist to publish an account of
attempts in this direction was Oerstedt, who published a paper
in 1824 in a Swedish periodical.* Oerstedt's original paper is
thus translated into Berzelius's " Jahresbericht :"f
" Oerstedt mixes calcined and pure alumina, quite freshly
prepared, with powdered charcoal, puts it in a porcelain retort,
ignites and leads chlorine gas through. The coal then reduces
the alumina, and there results aluminium chloride and carbonic
oxide, and perhaps also some phosgene, COCI2 ; the alumin-
ium chloride is caught in the condenser and the gases escape.
The sublimate is white, crystalline, melts about the tempera-
ture of boiling water, easily attracts moisture, and evolves heat
* Oversigt over det K. Danske Videnskabemes Selkabs Forhandlingar og dets
Medlemmers Arbeider. May, 1824, to May, 1825, p. 15.
fBerz. Jahresb. der Chemie, 1827, vi. 1 1 8.
(246)
REDUCTION OF ALUMINIUM COMPOUNDS. 247
when in contact with water. If it is mixed with a concentrated
potassium amalgam and heated quickly, it is transformed ; there
results potassium chloride, and the aluminium unites with the
mercury. The new amalgam oxidizes in the air very quickly,
and gives as residue when distilled in a vacuum a lump of metal
resembling tin in color and lustre. In addition, Oerstedt found
many remarkable properties of the metal and of the amalgam,
but he holds them for a future communication after further in-
vestigation."
Oerstedt did not publish any other paper, and the next ad-
vance in the science is credited to Wohler, whom all agree in
naming as the true discoverer of the metal.
Wohler' s Experiments (1827).
In the following article from Poggendorff 's Annalen,* Wohler
reviews the article of Oerstedt's given above, and continues as
follows : —
" I have repeated this experiment of Oerstedt, but achieved
no very satisfactory result. By heating potassium amalgam
with aluminium chloride and distilling the product, there re-
mained behind a gray, melted mass of metal, but which, by
raising the heat to redness, went ofif as green vapor and distilled
as pure potassium. I have therefore looked around for another
method or way of conducting the operation, but, unpleasant as
it is to say it, the reduction of the aluminium fails each time.
Since, however, Herr Oerstedt remarks at the end of his paper
that he did not regard his investigations in aluminium as yet
ended, and already several years have passed since then, it
looks as if I had taken up one of those researches begun aus-
piciously by another (but not finished by him), because it
promised new and splendid results. I must remark, however,
that Herr Oerstedt has indirectly by his silence encouraged me
to try to attain to further results myself. Before I give the art
how one can quite easily reduce the metal, I will say a few
words about aluminium chloride and its production (see p. 152).
* Pogg. Ann., 1827, ii. 147.
248 ALUMINIUM.
" I based the method of reducing aluminium on the reaction
of aluminium chloride on potassium, and on the property of the
metal not to oxidize in water. I warmed in a glass retort a
small piece of the aluminium salt with some potassium, and the
retort was shattered with a strong explosion. I tried then to do
it in a small platinum crucible, in which it succeeded very well.
The reaction is always so violent that the cover must be weighted
down, or it will be blown off; and at the moment of reduction,
although the crucible be only feebly heated from outside, it
suddenly glows inside, and the platinum is almost torn by the
sudden shocks. In order to avoid any mixture of platinum
with the reduced aluminium, I next made the reduction in a
porcelain crucible, and succeeded then in the following manner :
Put in the bottom of the crucible a piece of potassium free from
carbon and oil, and cover this with an equal volume of pieces
of aluminium chloride. Cover and heat over a spirit lamp, at
first gently, that the crucible be not broken by the production of
heat inside, and then heat stronger, at last to redness. Cool,
and when fully cold put it into a glass of cold water. A gray
powder separates out, which on nearer observation, especially
in sunlight, is seen to consist of little flakes of metal. After it
has separated, pour off the solution, filter, wash with cold
water, and dry; this is the aluminium."
In reality, this powder possessed no metallic properties, and
moreover, it contained potassium and aluminium chloride,
which gave it the property of decomposing water at 100°. To
avoid the loss of aluminium chloride by volatilization at the
high heat developed during the reaction, Liebig afterwards
made its vapors pass slowly over some potassium placed in a
long glass tube. This device of Liebig is nearly the arrange-
ment which Wohler adopted later, in 1845, ^nd which gave him
much better results.
Wbklcr's Experiments ( 1 845 ) .
The following is Wohler's second paper published in 1845 ■*
* Liebig's Annalen, 53, 422.
REDUCTION OF ALUMINIUM COMPOUNDS. 249
" On account of the violent incandescence with which the
reduction of aluminium chloride by potassium is accompanied,
this operation requires great precautions, and can be carried
out only on a small scale. I took for the operation a platinum
tube, in which I placed aluminium chloride, and near it some
potassium in a platinum boat. I heated the tube gently at first,
then to redness. But the reduction may also be done by put-
ting potassium in a small crucible, which is placed inside a
larger one, and the space between the two filled with aluminium
chloride. A close cover is put over the whole, and it is heated.
Equal volumes ot potassium and the aluminium salt are the
best proportions to employ. After cooling, the tube or cruci-
ble is put in a vessel of water. The metal is obtained as a gray
metallic powder, but on closer observation one can see even
with the naked eye small tin-white globules, some as large as
pins' heads. Under the microscope magnifying two hundred
diameters, the whole powder resolves itself into small globules,
several of which may sometimes be seen sticking together,
showing that the metal was melted at the moment of reduction.
A beaten-out globule may be again melted to a sphere in a
bead of borax or salt of phosphorus, but rapidly oxidizes dur-
ing the operation, and if the heat is continued, disappears
entirely, seeming either to reduce boric acid in the borax bead,
or phosphoric acid in the salt of phosphorus bead. I did not
succeed in melting together the pulverulent aluminium in a
crucibe with borax, at a temperature which would have melted
cast-iron, for the metal disappeared entirely and the borax be-
came a black slag. It seems probable that aluminium, being
lighter than molten borax, swims on it and burns. The white
metallic globules had the color and lustre of tin. It is perfectly
malleable and can be hammered out to the thinnest leaves.
Its specific gravity, determined with two globules weighing 32
milligrammes, was 2.50, and with three hammered- out globules
weighing 34 milligrammes, 2.67. On account of their lightness
these figures can only be approximate. It is not magnetic,
remains white in the air, decomposes water at 100°, not at
250 ALUMINIUM.
usual temperatures, and dissolves completely in caustic potash
(KOH). When heated in oxygen almost to melting, it is only
superficially oxidized, but it burns like zinc in a blast-lamp
flame."
These results of Wohler's, especially the determination of
specific gravity, were singularly accurate when we consider
that he established them working with microscopic bits of
the metal, It was just such work that established Wohler's
fame as an investigator. However, we notice that his metal
differed from aluminium as we know it in several important
respects, in speaking of which Deville says: "All this time
the metal obtained by Wohler was far from being pure ; it was
very difficultly fusible, owing, without doubt, to the fact that
it contained platinum taken from the vessel in which it had
been prepared. It. is well known that these two metals com-
bine very easily at a gentle heat. Moreover, it decomposed
water at 100°, which must be attributed either to the presence
of potassium or to aluminium chloride, with which the metal
might have been impregnated : for aluminium in presence of
aluminium chloride in effect decomposes water with evolution
of hydrogen."
After Wohler's paper in 1845, the next improvement is that
introduced by Deville in 1854-55, and this is really the date at
which aluminium, the metal, became known and its true proper-
ties established.
Deville s Experiments (1854).
The results of this chemist's investigations and success in
obtaining pure aluminium were first made public at the seance
of the French Academy, August 14, 1854, and included men-
tion of an electrolytic method of reduction (see Chap. XI.), as
well as of the following on reduction by sodium.*
" The following is the best method for obtaining aluminium
chemically pure in the laboratory. Take a large glass tube
about four centimeters in diameter, and put into it 200 or 300
* Ann. de Phys. et de Chim., xliii. 24.
REDUCTION OF ALUMINIUM COMPOUNDS. 2$ I
grammes of pure aluminium chloride free from iron, and isolate
it between two stoppers of amianthus (fine, silky asbestos).
Hydrogen, well dried and free from air, is brought in at one
end of the tube. The aluminium chloride is heated in this cur-
rent of gas by some lumps of charcoal in order to drive ofif
hydrochloric acid or sulphides of chlorine or of silicon, with
which it is always impregnated. Then there are introduced into
the tube porcelain boats, as large as possible, each containing
several grammes of sodium, which was previously rubbed quite
dry between leaves of filter paper. The tube being full of
hydrogen, the sodium is melted, the aluminium chloride is
heated and distils, and decomposes in contact with the sodium
with incandesence, the intensity of which can be moderated at
pleasure. The operation is ended when all the sodium has dis-
appeared, and when the sodium chloride formed has absorbed
so much aluminium chloride as to be saturated with it. The
aluminium which has been formed is held in the double chloride
of sodium and aluminium, AlClg.NaCl, a compound very fusible
and very volatile. The boats are then taken from the glass
tube, and their entire contents put in boats made of retort car-
bon, which have been previously heated in dry chlorine in order
to remove all siliceous and ferruginous matter. These are then
introduced into a large porcelain tube, furnished with a pro-
longation and traversed by a current of hydrogen, dry and free
from air. This tube being then heated to bright redness, the
aluminium-sodium chloride distils without decomposition and
condenses in the prolongation. There is found in the boats,
after the operation, all the aluminium which had been reduced,
collected in at most one or two small buttons. The boats when
taken from the tube should be nearly free from aluminium-
sodium chloride, and also from sodium chloride. The buttons
of aluminium are united in a small earthenware crucible, which
is heated as gently as possible, just sufificient to melt the metal.
The latter is pressed together and skimmed clean by a small
rod or tube of clay. The metal thus collected may be very
suitably cast in an ingot mould."
252 ALUMINIUM.
The later precautions added to the above given process were
principally directed towards avoiding the attacking of the cruci-
ble, which always takes place when the metal is melted with a
flux, and the aluminium thereby made more or less siliceous.
The year following the publication of these results, this labora-
tory method was carried out on a large scale at the chemical
works at Javel.
Deville's Methods (1855).
The methods about to be given are those which were devised
in Deville's laboratory at the Ecole Normale, during the winter
of 1854-55, and applied on a large scale at Javel, during the
spring of 1855 (March-July). The Emperor Napoleon III.
defrayed the expenses of this installation. Descriptions of the
methods used for producing alumina, aluminium chloride and
sodium at Javel can be found under their respective headings
(pp. 134, 153, 180), We here confine our description to
the mode of reducing the aluminium chloride by sodium, and
the remarks incident thereto. The process has at present
only an historic interest, as it was soon modified in its details
so as to be almost entirely changed. The following is Deville's
description : —
" Perfectly pure aluminium. — To obtain aluminium perfectly
pure it is necessary to employ materials of absolute purity, to
reduce the metal in presence of a completely volatile flux, and
finally never to heat, especially with a flux, in a siliceous vessel
to a high temperature.
" Pure materials. — The necessity of using absolutely pure
materials is easy to understand ; all the metallic impurities are
concentrated in the aluminium, and unfortunately I know no
absolute method of purifying the metal. Thus, suppose we
take an alum containing o.i per cent, of iron and 11 per cent,
of alumina; the alumina derived from it will contain i per
cent, of iron, and supposing the alumina to give up all the alu-
minium in it, the metal will be contaminated with 2 per cent,
of iron.
REDUCTION OF ALUMINIUM COMPOUNDS.
253
'^Influence of flux or slag. — The flux, or the product of the
reaction of the sodium on the aluminous material, ought to be
volatile, that one may separate the aluminium by heat from the
material with which it has been in contact, and with which it
remains obstinately impregnated because of its small specific
gravity.
" Influence of the vessel. — The siliceous vessels in which
aluminium is received or melted give it necessarily a large
quantity of silicon, a very injurious impurity. Silicon cannot
be separated from aluminium by any means, and the siliceous
aluminium seems to have a greater tendency to take up more
silicon than pure aluminium, so that after a small number of
remeltings in siliceous vessels the metal becomes so impure as
to be almost infusible.
In order to avoid the dangers pointed out above, Deville re-
commended following scrupulously the following details in
order to get pure aluminium.
" Reduction of solid sodium. — The crude aluminium chloride
placed in the cyHnder A (Fig. 23), is vaporized by the fire and
,-JL,
Fig. 24.
r
1
I to.»»iaa Y^s;^ teMaa "T
passes through the tube to the cylinder B, containing 60 to 80
kilos of iron nails heated to a dull-red heat. The iron retains
as relatively fixed ferrous chloride, the ferric chloride and
hydrochloric acid which contaminate the aluminium chloride,
and likewise transforms any sulphur dichloride (SCl^) in it into
ferrous chloride and sulphide of iron. The vapors on passing
out of B through the tube, which is kept at about 300°, deposit
254 ALUMINIUM.
spangles of ferrous chloride, which is without sensible tension
at that temperature. The vapors then enter D, a cast-iron
cylinder in which are three cast-iron boats each containing 500
grms. of sodium. It is sufficient to heat this cylinder barely to
a dull-red heat in its lower part, for the reaction once com-
menced disengages enough heat to complete itself, and it is
often necessary to take awav all the fire from it. There is at
first produced in the first boat some aluminium and some sod-
ium chloride, which latter combines with the excess of alumin-
ium chloride to form the volatile aluminium-sodium chloride,
AlClj.NaCl. These vapors of double chloride condense on the
second boat and are decomposed by the sodium into alumin-
ium and sodium chloride. A similar reaction takes place in
the third boat when all the sodium of the second has disap-
peared. When on raising the cover it is seen that the
sodium of the last boat is entirely transformed into a lumpy
black material, and that the reactions are over, the boats
are taken out, immediately replaced by others, and are al-
lowed to cool covered by empty boats. In this first opera-
tion the reaction is rarely complete, for the sodium is
protected by the layer of sodium chloride formed at its ex-
pense. To make this disappear, the contents of the boats are
put into cast-iron pots or earthen crucibles, which are heated
until the aluminium chloride begins to volatilize, when the so-
dium will be entirely absorbed and the aluminium finally re-
mains in contact with a large excess of its chloride, which is
indispensable for the success of the operation. Then the pots
or crucibles are cooled, and there is taken from the upper part
of their contents a layer of sodium chloride almost pure, while
underneath are found globules of aluminium which are sepa-
rated from the residue by washing with water. Unfortunately
the water in dissolving the aluminium chloride of the flux exer-
cises on the metal a very rapid destructive action, and only
the globules larger than the head of a pin are saved from this
washing. These are gathered together, dried, melted in an
earthen crucible, and pressed together with a clay rod.
REDUCTION OF ALUMINIUM COMPOUNDS. 255
The button is then cast in an ingot mould. It is important in
this operation to employ only well-purified sodium, and not to
melt the aluminium if it still contains any sodium, for in this
case the metal takes fire and burns as long as any of the alka-
line metal remains in it. In such a case it is necessary to re-
melt in presence of a little aluminium-sodium chloride.
" Such is the detestable process by means of which were made
the ingots of aluminium sent to the Exhibition (1855). To
complete my dissatisfaction at the processs, pressed by time and
ignorant of the action of copper on aluminium, I employed in
almost all my experiments reaction cylinders and boats of cop-
per, so that the aluminium I took from them contained such
quantities of this metal as to form a veritable alloy. Moreover, it
had lost almost all ductility and malleability, had a disagreeable
gray tint, and finally at the end of two months it tarnished by
becoming covered with a black layer of oxide or sulphide of
copper, which could only be removed by dipping in nitric acid.
But, singular to relate, an ingot of virgin silver which had been
put alongside the aluminium that the public might note easily
the difference in color and weight of the two metals, was
blackened still worse than the impure aluminium. Only one of
the bars exhibited, which contained no copper, remained un-
altered from the day of its manufacture till now (1859). It
was some of this cupreous aluminium that I sent to M.
Regnault, who had asked me for some in order to determine its
specific heat. I had cautioned him at the time of the number
and nature of the impurities which it might contain, and the
analysis of M. Salvetat, which is cited in the memoir of
Regnault, accords with the mean composition of the specimens
that I had produced and analyzed at that time (see p. 54,
Analysis i). It is to be regretted that I gave such impure
material to serve for determinations of such splendid precision.
I was persuaded to do so only by the entreaties of M.
Regnault, who could not wait until I prepared him better. It is
also this cupreous aluminium which M. Hulot has called ' hard
aluminium,' in a note on the physical properties of this metal
256 ALUMINIUM.
which he addressed to the Academy. Hulot has remarked
that this impure metal, which is crystalline in structure, after
having been compressed between the dies of the coining press
may lose its crystalline structure, to which it owes its brittle-
ness, and become very malleable. It possesses then such
strength that it works well in the rolls of a steel rolling mill.
Further, this 'hard aluminium' becomes quite unalterable when
it has thus lost its texture.
"Reduction by sodium vapor. — This process, which I have not
perfected, is very easy to operate, and gave me very pure metal
at the first attempt. I operate as follows : I fill a mercury bot-
tle with a mixture of chalk, carbon, and carbonate of soda, in
the proportions best for generating sodium. An iron tube
about ten centimetres long is screwed to the bottle, and the
whole placed in a wind furnace, so that the bottle is heated to
red-white and the tube is red to its end. The end of the tube
is then introduced into a hole made in a large earthen crucible
about one-fourth way from the bottom, so that the end of the
tube just reaches the inside surface of the crucible. The car-
bonic oxide (CO) disengaged burns in the bottom of the cru-
cible, heating and drying it ; afterwards the sodium flame
appears, and then pieces of aluminium chloride are thrown into
the crucible from time to time. The salt volatilizes and de-
composes before this sort of tuyere, from which issues the
reducing vapor. More aluminium salt is added when the
vapors coming from the crucible cease to be acid, and when
the flame of sodium burning in the atmosphere of aluminium
chloride loses its brightness. When the operation is finished,
the crucible is broken and there is taken from the walls below
the entrance of the tube a saline mass composed of sodium
chloride, a considerable quantity of globules of aluminium, and
some sodium carbonate, which latter is in larger quantity the
slower the operation was performed. The globules are de-
tached by plunging the saline mass into water, when it be-
comes necessary to notice the reaction of the water on litmus.
If the water becomes acid, it is renewed often ; if alkaline, the
REDUCTION OF ALUMINIUM COMPOUNDS. 257
mass, impregnated with metal, must be digested in nitric acid,
diluted with three or four volumes of water, and so the metal is
left intact. The globules are reunited by melting with the
precautions before given."
Deville's Process (1859).
The process then in use at Nanterre was based on the use of
aluminium-sodium chloride, which was reduced by sodium,
with cryolite or fluorspar as a flux. The methods of preparing
each of these materials were carefully studied out at the chem-
ical works of La Glaciere, where, from April, 1856, to April,
1857, the manufacture of aluminium was carried on by a com-
pany formed by Deville and a few friends, and from thence
proceeded the actual system which was established at Nanterre
under the direction of M. Paul Morin when the works at La
Glaciere were closed. The methods of preparation of alumina,
aluminium-sodium chloride and sodium used at Nanterre are
placed under their respective, headings (pp. 137, 154, 190).
In the first year that the works at Nanterre were in opera-
tion there were made :
Aluminium-sodium chloride 10,000 kilos.
Sodium 2,000 "
Aluminium 600 "
The metal prepared improved constantly in quality, M. Morin
profiting continually by his experience and improving the
practical details constantly, so that the aluminium averaged, in
1859, gj per cent. pure. (See Analysis 9, p. 54.)
As to the rationale of the process used, aluminium chloride
was replaced by aluminium-sodium chloride because the latter
is less deliquescent and less difficult of preservation ; but the.
small amount of moisture absorbed by the double chloride is
held very energetically, at a high temperature giving rise to
some alumina, which encloses the globules of metal with a thin
coating, and so hinders their easy reunion to a button. Deville
remarked that the presence of fluorides facilitated the reunion
17
258 ALUMINIUM.
of these globules, which fact he attributed to their dissolving
the thin coat of alumina ; so that the employment of a fluoride
as a flux became necessary to overcome the effect produced
primarily by the aluminium-sodium chloride holding moisture
so energetically. Deville gives the following account of the
development of these improvements : "The facility with which
aluminium unites in fluorides is due without doubt to the prop-
erty which these possess of dissolving the alumina on the sur-
face of the globules at the moment of their formation, and
which the sodium is unable to reduce. I had experienced great
difificulty by obtaining small quantities of metal poorly united,
when I reduced the aluminium-sodium chloride by sodium ;
M. Rammelsberg, who often made the same attempts, tells me
he has had a Hke experience. But I am assured by a scrupu-
lous analysis that the quantity of metal reduced by the sodium
is exactly that which theory indicates, although after many
operations there is found only a gray powder, resolving itself
under the microscope into a multitude of small globules. The
fact is simply that aluminium-sodium chloride is a very poor
flux for aluminium. MM. Morin, Debray, and myself have
undertaken to correct this bad effect by the introduction of a
solvent for the alumina into the saline slag which accompanies
the aluminium at the moment of its formation. At first, we
found it an improvement to condense the vapors of aluminium
chloride, previously purified by iron, directly in sodium chloride,
placed for this purpose in a crucible and kept at a red heat.
We produced in this way, from highly colored material, a double
chloride very white and free from moisture, and furnishing on
reduction a metal of fine appearance. We then introduced
fluorspar (CaF^) into the composition of the mixture to be
reduced, and we obtained good results with the following pro-
portions :
Aluminium-sodium chloride 400 grammes.
Sodium chloride 200 "
Calcium fluoride 200 "
Sodium 75 to 80 "
REDUCTION OF ALUMINIUM COMPOUNDS. 259
" The double chloride ought to be melted and heated almost
to low red heat at the moment it is employed, the sodium
chloride calcined and at a red heat or melted, and the fluorspar
pulverized and well dried. The double chldride, sodium chlor-
ide and calcium fluoride are mixed and alternated in layers in
the crucible with sodium. The top layer is of the mixture, and
the cover is sodium chloride. Heat gently, at first, until the
reaction ends, and then to a heat about sufficient to melt silver.
The crucible, or at least that part of it which contains the mix-
ture, ought to be of a uniform red tint, and the material per-
fectly liquid. It is stirred a long time and cast on a well dried,
chalked plate. There flows out first a very limpid liquid, col-
orless and very fluid ; then a gray material, a little more pasty,
which contains aluminium in little grains, and is set aside ; and
finally a button with small, metallic masses which of them-
selves ought to weigh 20 grms. if the operation has succeeded
well. On pulverizing and sieving the gray slag, 5 or 6 grms.
of small globules are obtained, which may be pressed together
by an earthen rod in an ordinary crucible heated to redness.
The globules are thus reunited, and when a sufficient quantity
is collected the metal is cast into ingots. In a well-conducted
operation, 75 grms. of sodium ought to give a button of 20
grms. and S grms. in grains, making a return of one part alu-
minium from three of sodium. Theory indicates one to two
and a half, or 30 grms. of aluminium from 75 of sodium. But
all the efforts which have been made to recover from the inso-
luble slag the 4 or 5 grms. of metal not united, but easily vis-
ible with a glass, have been so far unsuccessful. There is,
without doubt, a knack, a particular manipulation, on which de-
pends the success of an operation which would render the
theoretical amount of metal, but we lack it yet. These opera-
tions take place, in general, with more facility on a large scale,
so that we may consider fluorspar as being suitable for serving
in the manufacture of aluminium in crucibles. We employed
very pure fluorspar, and our metal was quite exempt from
silicon. It is true that we took a precaution which is necessary
260 ALUMINIUM.
to adopt in operations of this kind ; we plastered our crucibles
inside with a layer of aluminous paste, the composition of
which has been given in 'Ann. de Chim. et de Phys.' xlvi. 195.
This paste is made of calcined alumina and an aluminate of
lime, the latter obtained by heating together equal parts of
chalk and alumina to a high heat. By taking about four parts
calcined alumina and one of aluminate of lime well pulverized
and sieved, moistening with a little water, there is obtained a
paste with which the inside of an earthen crucible is quickly
and easily coated. The paste is spread evenly with a porcelain
spatula, and compressed strongly until its surface has become
well polished. It is allowed to dry, and then heated to bright
redness to season the coating, which does not melt, and pro-
tects the crucible completely against the action of the alumin-
ium and fluorspar. A crucible will serve several times in suc-
cession, provided that the new material is put in as soon as the
previous charge is cast. The advantages of doing this are
that the mixture and the sodium are put into a crucible al-
ready heated up, and so lose less by volatilization because the
heating is done more quickly, and the crucible is drier than if
a new one had been used or than if it had been let cool. A
new crucible should be heated to at least 300° or 400° before
being used. The saline slag contains a large quantity of cal-
cium chloride, which can be washed away by water, and an in-
soluble material from which aluminium fluoride can be volatil-
ized.
" Yet the operation just described, which was a great im-
provement on previous ones, requires many precautions and a
certain skill of manipulation to succeed every time. But
nothing is more easy or simple than to substitute cryolite for
the fluorspar. Then the operation is much easier. The
amount of metal produced is not much larger, although the
button often weighs 22 grammes, yet if cryolite can only be ob-
tained in abundance in a continuous supply, the process which
I will describe will become most economical. The charge is
made up as before, except introducing cryolite for fluorspar.
REDUCTION OF ALUMINIUM COMPOUNDS. 26 1
In one of our operations we obtained, with -j^ grms. of sodium,
a button weighing 22 grms. and 4 grms. in globules, giving a
yield of one part aluminium to two and eight-tenths parts
sodium, which is very near to that indicated by theory. The
metal obtained was of excellent quality. However, it con-
tained a little iron coming from the aluminium chloride, which
had not been purified perfectly. But iron does not injure the
properties of the metal as copper does ; and, save a little bluish
coloration, it does not alter its appearance or its resistance to
physical and chemical agencies.
" After these attempts we tried performing the reduction sim-
ply on the bed of a reverberatory furnace, relying on the imme-
diate reaction of sodium on the double chloride to use up these
materials before they could be perceptibly wasted by the fur-
nace gases. This condition was realized in practice with
unlooked-for success. The reduction is now made on a some-
what considerable scale at the Nanterre works, and never, since
commencing to operate in this way, has a reduction failed, the
results obtained being always uniform. The furnace now used
has all the relative dimensions of a soda furnace. In fact,
almost the temperature of an ordinary soda furnace is required
that the operation may succeed perfectly. The absolute dimen-
sions of the furnace, however, may vary with the quantity of alu-
minium to be made in one operation, and are not limited. With
a bed of one square metre surface, 6 to 10 kilos of aluminium
can be reduced at once ; and since each operation lasts about
four hours, and the furnace may be recharged immediately after
emptying it of the materials just treated, it is seen that, with so
small a bed, 60 to lOO kilos of aluminium can be made in
twenty-four hours without any difficulty. In this respect, I
think the industrial problem perfectly solved. The proportions
which we employed at first were —
Aluminium-sodium chloride (crushed) 10 parts.
Fluorspar 5 "
Sodium (in ingots) 2 "
" As aluminium is still very dear, it is necessary to direct
262 ALUMINIUM.
great attention to the return from the materials used, and on
this point there is yet much progress to be made. We ascer-
tained many times that the return was always a little better, and
the reunion of the metal to a single ingot a little easier, when
cryolite was substituted for fluorspar, the price of the former,
after having been high, being now lowered to 350 francs per
tonne (about $75 per long ton). For this reason we can now
use cryolite instead of fluorspar, and in the same proportions.
We can also recover alumina from this cryolite by treating the
slags (see p. 148). The double chloride and pulverized cryo-
lite are now mixed with the sodium in small ingots, and the
mixture thrown on to the bed of the heated-up furnace. The
dampers are then shut, to prevent as much as possible access
of air. Very soon a lively reaction begins, with the production
of such heat that the brick sides of the furnace, as well as the
materials on the hearth, are made bright red-hot. At this heat
the mixture is almost completely fused. Then it is necessary
to open the damper and direct the flame on the bed in such
manner as to heat the bath equally all over and unite the re-
duced aluminium. When the operation is considered ended, a
casting is made by an opening in the back of the furnace and
the slag is received in cast-iron pots. At the end of the cast
the aluminium arrives in a single jet, which unites into a single
lump at the bottom of the still-liquid slag. The gray slag flow-
ing out last should be pulverized and sieved, to extract the
divided globules of aluminium, 200 to 300 grammes of which
can sometimes be extracted from one kilo of gray slag. The
pulverization of the slag is in all cases indispensable in its sub-
sequent treatment for extracting its alumina. The slag is of
two kinds, one fluid and light, which covered the bath, and is
rich in sodium chloride ; the other less fusible and pasty, gray
in color, which is more dense and lies in contact with the alu-
minium. The coloring material producing the grayness is car-
bon, coming either from the sodium or from the oil which im-
pregnated it, or finally from the vapor of the oil. I attribute
the slight pastiness of this slag to a little alumina dissolved by
the fluorides. This slag contains about:
REDUCTION OF ALUMINIUM COMPOUNDS. 263
Sodium chloride 60 parts.
Aluminium fluoride 40 "
and on washing it the former dissolves while the latter remains,
mixed with a little cryolite or alumina. This is the alumina
which had been dissolved or retained in the bath of fluoride.
It will be remarked that the bath of slag contains no other
fluoride than aluminium fluoride, which does not attack earthen
crucibles or siliceous materials in general except at a very high
temperature. It is for this reason that the hearth and other parts
of the furnace resist easily a fluoride slag containing only alu-
minium fluoride, which has not the property of combining with
silicon fluoride at the expense of the silica of the bricks — as
sodium fluoride does in like circumstances. In our operations,
cryolite is used only as a flux. In the process of reduction
based on cryolite alone, the sodium fluoride resulting is, on the
contrary, very dangerous to crucibles, and it is due to that fact
especially that the aluminium absorbs a large quantity of
silicon, which always happens with this method. In fact, it is
well known that metallic silicon can be prepared in this way by
prolonging the operation a little."
Deville closes his account of the aluminium industry in 1859
with these words : " Many things yet remain to us to do, and
we can scarcely say now that we know the true qualities of the
substances we employ. But the matter is so new, is harassed
with so many difiSculties even after all that has been done, that
our young enterprise may hope everything from the future when
it shall have acquired experience. I ought to say, however,
that the aluminium industry is now at such a point that if the
uses of the metal are rapidly extended it may change its aspect
with great rapidity. One may ask to-day how much a kilo of
iron would cost if a works made only 60 to 100 kilos of it a
month, if large apparatus were excluded from this industry, and
iron obtained by laboratory processes which would permit it to
become useful only by tedious after-treatment. Such will not
be the case with aluminium, at least with the processes just de-
scribed. In fact in all I undertook, either alone or with my
264 ALUMINIUM.
friends, I have always been guided by this thought — that we
ought to adopt only such apparatus as is susceptible of being
immediately enlarged, and to use only materials almost as com-
mon as clay itself for the source of the aluminium."
The Deville Process (1882).
The process just described reached a fair degree of perfec-
tion at Nanterre, under the direction of M. Paul Morin. After-
wards, some of the chemical operations incidental to the
process were carried on at the works of the Chemical Manufac-
turing Company of Alais and Carmargue, at Salindres (Gard),
owned by H. Merle & Co. At a later date the whole manufac-
ture was removed to this place, while the Societe Anonyme de
1' Aluminium, at Nanterre, worked up the metal, and placed it
on the market. The Salindres works, about 1880, went under
the management of A. R. Pechiney & Co., and under the per-
sonal attention of M. Pechiney, the Deville process reached its
perfection. The following account is taken mostly from M.
Margottet's article on aluminium in Fremy's Encyclopedic
Chimique.
An outline of the process, as it was prepared, may very
appropriately be given at this place, although detailed descrip-
tions of the preliminary processes for preparing the materials
for reduction are given under the appropriate headings (see
pp. 137, 154, 190).
The primary material to furnish the aluminium is bauxite.
To obtain the metal it is necessary to proceed successively
through the following operations: —
I. Preparation of the aluminate of soda, and solution of this
salt to separate it from the ferric oxide contained in the
bauxite.
II. Precipitation of hydrated alumina from the aluminate of
soda by a current of carbon dioxide ; washing the precipitate.
III. Preparation of a mixture of alumina, carbon, and salt,
drying it, and then treating with gaseous chlorine to obtain the
double chloride of aluminium and sodium.
REDUCTION OF ALUMINIUM COMPOUNDS. 265
IV. Lastly, treatment of this chloride by sodium to obtain
aluminium.
The principal chemical reactions on which this process rests
are the following: —
Formation of aluminate of soda by calcining bauxite with
sodium carbonate —
(AlFe) A.2H,0 + 3Na,C03=-Al,03-3Na,0 + Fe.Oa
+ 2H,0 + 3CO,.
Formation of alumina by precipitating the aluminate of soda
with a current of carbon dioxide —
Al,03-3Na,0 + 3CO, + 3H,0 = Al.Os.sH.O + 3Na,C03.
Formation of aluminium-sodium chloride by the action of
chlorine on a mixture of alumina, carbon, and sodium chloride —
AI2O3 + 3C + 2NaCl + 6C1 = 2 (AlCla.NaCl) + 3CO.
Reduction of this double chloride by sodium —
AlCIs.NaCl + 3Na = Al + 4NaCl.
As observed before, we will here consider only the last oper-
ation. The advances made since 1859 are mostly in matters of
detail, which every one knows are generally the most import-
ant part of a process ; and so, although a few of the details
may be repeated, yet we think it best not to break the contin-
uity of this description by excising those few sentences which
are nearly identical in the two accounts.
The difiSculty of this operation, at least from an industrial
point of view, is to get a slag fusible enough and light enough
to let the reduced metal easily sink through it and unite.
This result has been reached by using cryolite. This material
iorms with the sodium chloride resulting from the reaction a
very fusible slag, in the midst of which the aluminium collects
well, and falls to the bottom. In one operation the charge is
now composed of —
266 ALUMINIUM.
100 kilos Aluminium-sodium chloride.
45 " Cryolite.
35 " Sodium.
The double chloride and cryolite are pulverized, the sodium^
cut into small pieces a little larger than the thumb, is divided
into three equal parts, each part being put into a sheet-iron
basket. The mixture of double chloride and cryolite, being
pulverized, is divided into four equal parts, three of these are
respectively put in each basket with the sodium, the fourth
being placed in a basket by itself. The reduction furnace (see
Fig. 25.
r
a.
Fig. 25) is a little furnace of refractory brick, with an inclined
hearth and a vaulted roof. This furnace is strongly braced by
iron tie-rods, because of the concussions caused by the reac-
tion. The flame may at any given moment be directed into a.
flue outside of the hearth. At the back part of the furnace,,
that is to say, on that side towards which the bed slopes, is a
little brick wah which is built up for each reduction and is.
taken away in operating the running out of the metal and slag>
A gutter of cast-iron is placed immediately in front of the wall
to facilitate running out the materials. All this side of the fur-
nace ought to be opened or closed at pleasure by means of a
damper. Lastly, there is an opening for charging in the roof,
closed by a lid. At the time of an operation the furnace
should be heated to low redness, then are introduced in rapid
REDUCTION OF ALUMINIUM COMPOUNDS. 267
succession the contents of the three baskets containing sodium,
etc., and lastly the fourth containing only double chloride and
no sodium. Then all the openings of the furnace are closed,
and a very vivid reaction accompanied by dull concussions im-
mediately takes place. At the end of fifteen minutes, the ac-
tion subsides, the dampers are opened and the heat continued,
meanwhile stirring the mass from time to time with an iron
poker. At the end of three hours the reduction is ended, and
the metal collects at the bottom of the liquid bath. Then the
running out is proceeded with in three phases : First — Running
off the upper part of the bath, which consists of a fluid material
completely free from reduced aluminium and constituting the
white slag. To run this out a brick is taken away from the
upper course of the little wall which terminates the hearth.
These slags are received in an iron wagon. Second — Running
out the aluminium. This is done by opening a small orifice
left in the bottom of the brick wall, which was temporarily
plugged up. The liquid metal is received in a cast-iron melt-
ing pot, the bottom of which has been previously heated to
redness. The aluminium is immediately cast in a series of
small rectangular cast-iron moulds. Third — Running out of
the rest of the bath, which constitutes the gray slags. These
were, like the white slags, formed by the sodium chloride and
cryolite, but they contain, in addition, isolated globules of alu-
minium. To run these out, all the bricks of the little wall are
taken away.. , This slag is received in the same melting pot into
which the aluminium was run, the latter having been already
moulded. Here it cools gradually, and after cooling there are
always found at the bottom of the pot several grains of metal.
In a good operation there are taken from one casting 10.5
kilos of aluminium, which is sold directly as commercial metal.
The following data as to the expense of this process may be
very appropriately inserted here, giving the cost at Salindres in
1873, in which year 3600 kilos are said to have been made.
* Manufacture of one kilo of aluminium.
* A. Wurtz, Wagner's Jahresb., 1874, vol. xxi.
268 ALUMINIUM.
Sodium 3.44 kilos @ 11.32 fr. per kilo = 38 fr. 90 cent.
Aluminium-sodium
chloride. . . . 10.04 " 2.48 " " = 24 " 90 "
Cryolite 3.87 " 61.0 " 100 kilos ^ 2 " 36 "
Coal 29.17 " 1.40 " " = o " 41 "
Wages I " 80 "
Costs o " 88 "
Total 69 " 25 "
This must be increased ten per cent, for losses and other ex-
penses, making the cost of aluminium 80 fr. per kilo, and it is
sold for 100. ($9.00 per lb.)
According to a statement in the ' Bull, de la Soc. de I'lndustrie
Minerale,' ii. 451, made in 1882, Salindres was then the only
place in which aluminium was being manufactured. The
Deville process was finally driven out of the market, and the
manufacture at Salindres suspended, in 1890.
Niewerth's Process (1883).
This method can be regarded as little more than a suggestion,
since it follows exactly the lines of some of Deville's earlier ex-
periments. Although theoretically very advantageous, yet in
practice it has probably been found far inferior in point of yield
of metal and expense to the ordinary sodium processes. The
patent is taken out in the United States and other countries in
the name of H. Niewerth, of Hanover, and is thus summarized :
*A compound of aluminium, with chlorine or fluorine, is
brought by any means into the form of vapor, and conducted,
strongly heated, into contact with a mixture of 62 parts sodium
carbonate, 28 coal, and 10 chalk, which is also in a highly heated
condition. This mixture disengages sodium, which reduces the
gaseous chloride or fluoride of aluminium, the nascent sodium
being the reducing agent. In place of the above mixture other
suitable mixtures which generate sodium may be employed, or
mixtures may also advantageously be used from which potassium
is generated.
* Sci. Am. Supple., Nov. 17, 1883.
REDUCTION OF ALUMINIUM COMPOUNDS. 269
Gadsden's Patent (1883).
H. A. Gadsden, of London, and E. Foote,* of New York,
were granted a patent based on the principle of heating in a
retort sodium carbonate and carbonaceous matter, or any suit-
able mixture for generating sodium, and conducting the vapor
of sodium produced into another retort, lined with carbon, in
which aluminium chloride, or aluminium-sodium chloride or
cryolite, has been placed and heated. The second English pat-
ent claims to heat a mixture which will generate sodium in one
retort, and pass chlorine over a mixture of carbon and alum-
ina, thus generating aluminium chloride, in another retort, and
then mixing the two vapors in a third retort or reaction
chamber.
Friskmuth's Process (1884).
This was patented in the United States in 1884 (U. S. Pat.
308,152, Nov. 1884). In what the originality of the process
consists, in view of Deville's publications and even in view of
the processes just mentioned, we cannot see. Col. Frishmuth
himself admitted, in 1887, having abandoned the sodium process,
as the difficulties of the method did not permit its competing
with the more roundabout but more easily-conducted operation
with solid sodium. A simple transcript of the claims in his
patent will give a sufficiently extended idea of the reactions
proposed to be used.
1. The simultaneous generation of sodium vapor and a vola-
tile compound of aluminium in two separate vessels or retorts,
and mingling the vapors thus obtained in a nascent ( ! ) state
in a third vessel, wherein they react on each other.
2. The sodium vapor is produced from a mixture of a sodium
compound and carbon, or some other reducing agent; and the
aluminous vapor from aluminous material.
3. The simultaneous generation of sodium vapor and vapor
of aluminium chloride or aluminium fluoride; or of sodium
vapor and aluminium-sodium chloride.
* English patents 1995 and 493° (1883); German patent 27,572 (1884).
2 70 ALUMINIUM.
4. Converting the aluminous material to a vapor by heating
it in a retort with sodium chloride, and subjecting it at the
same time to chlorine gas ; mingling the vapor of aluminium-
sodium chloride thus obtained with vapor simultaneously gen-
erated from sodium carbonate and carbon.
H. von Grousillier' s Improvement (1885)-
This suggestion as to the way of performing the reduction
by sodium is the subject of the English patent 7858, June 29,
18B5. Dr. Fischer remarks on it, in " Wagner's Jahresbericht"
for 1885, that "it is apparently wholly worked out at the
writing-table," The patentee. Hector von Grousillier, Springe,
Hanover, thus describes his invention :
" In order to avoid the difficulties ordinarily met with in the
use of aluminium-sodium chloride to obtain aluminium, I raise
the volatilizing point of aluminium chloride by performing its
reduction, either chemically or electrolytically, under pressure
in a strong hermetically-closed vessel, lined with clay or mag-
nesia, and provided with a safety valve."
The Deville-Castner Process (1886).
This last development of the old Deville process was ope-
rated by the Aluminium Company, Limited, at their large new
works at Oldbury, near Birmingham, England. The plant
covered nearly five acres of ground, and adjoined Chance Bros.'
large chemical works, from which the hydrochloric acid used
was obtained and the waste soda-liquors returned, by means of
large pipes connecting the two plants. The company was thus
in position to obtain acid and dispose of its by-products to
very good advantage. The principle on which the process was
worked is similar to its predecessor, in being the reduction of
aluminium-sodium chloride by sodium, but it improves on the
other in the cheaper production of both these materials. For
instance, the alumina used is obtained and converted into
double chloride by Mr. Webster's processes, by which the cost
of this salt is not over 3^. per lb. (see p. 164), as against i2d..
REDUCTION OF ALUMINIUM COMPOUNDS. 2/1
the cost at Salindres ; further, by Mr. Castner's sodium process
it is acknowledged that the sodium cost only about ^d. per lb.,
as against 48^^., or $1, as formerly. Since 10 lbs. of the chlo-
ride and 3 lbs. of sodium are required to produce i lb. of alu-
minium, the average saving in these two items, over the old
process, is somewhere about 75 per cent.
The works contain a sodium building, in which are four large
sodium furnaces, each capable of producing over 500 lbs. of
that metal in twenty-four hours ; the sodium is also remelted
and stored in the same building (see p. 215). The double
chloride furnaces are in a building 250 feet by 50 feet wide, there
being 12 furnaces, each containing 5 retorts. The total output
of double chloride is an average of 5000 lbs. per day. (See. p.
162). Connected with this building is a chlorine plant of the
largest size, capable of supplying about a ton and a half of
chlorine a day. In a separate building are two reverberatory
furnaces, in which the final reduction takes place and the alu-
minium is produced. Besides these there are a rolling mill,
wire mill, and foundry on the grounds. From the quantity of
sodium and double chloride produced, we can see that the
works can produce about 500 lbs. of aluminium a day, or
150,000 lbs. a year, with some sodium left over for sale or other
purposes.
The mode of conducting the reduction is not very different
from that practiced at Salindres. There are two regenerative
reverberatory furnaces used, one about twice as large as the
other. The larger furnace has a bed about six feet square, slop-
ing towards the front of the furnace, through which are several
openings at different heights. The charge for this furnace con-
sists of 1200 lbs. of double chloride, 350 lbs. of sodium, and
600 lbs. of cryolite for a flux. The chloride is in small pieces,
the cryolite is in powder, and the sodium is cut into thin slices
by a machine. These ingredients are put into a revolving
wooden drum placed on a staging over the furnace, and are
there thoroughly mixed. The drum is then opened and
turned, when the contents fall into a small wagon beneath.
272 ALUMINIUM.
The furnace having been raised to the required temperature, all
the dampers are shut and the car is moved on a track immedi-
ately over a. large hopper placed in the roof of the furnace.
The hopper being opened, the charge is dumped in and drops
on to the centre of the hearth. The reaction is immediate,
and the whole charge becomes liquid in a very short time.
After a few minutes, heating gas is again turned on, and the
furnace kept moderately hot for two or three hours. The reac-
tion has been
AlCla.NaCl + 3Na = Al + 4NaCl
and the aluminium gathers under the bath of cryolite and sod-
ium chloride. One of the lower tap-holes is then opened with
a bar, and the aluminium run out into moulds. When the
metal has all run out it is followed by slag, which flows into
iron wagons. The openings are then plugged up and the fur-
nace is ready for another charge. The charge given produces
usually 115 to 120 lbs. of aluminium, the whole operation last-
ing about 4 hours. The large furnace could thus produce 840-
lbs. in 24 hours, and the smaller one half that quantity. The
first portion of metal running out is the purest, the latter por-
tions, and especially that entangled in the slag on the hearth, and
which has to be scraped out, containing more foreign sub-
stances. This impure metal is about one-fourth of all the
aluminium in the charge.
The purity of the metal run out depends directly on the
purity of the chloride used. If the double chloride contains
0.2 per cent, of iron, the metal produced will very probably
contain all of it, or 2 per cent. Using the double chloride
purified by Mr. Castner's new method (see p. 163), by which
the content of iron is reduced to 0.05 per cent, or less, alu-
minium can be made containing less than 0.5 per cent, of iron
and from 99 to 99.5 per cent, of aluminium. Professor Roscoe
exhibited at one of his lectures a mass of metal weighing 116'
lbs., being one single running from the furnace, and which con-
tained only 0.3 per cent, of silicon and 0.5 per cent. iron. In.
REDUCTION OF ALUMINIUM COMPOUNDS. 273
practice, the metal from 8 or 10 runnings is melted down to-
gether to make a uniform quality.
Taking the figures given, it appears that the metal run out
represents 70 per cent, of the aluminium in the charge, and 80
percent, of the weight which the sodium put in should reduce;
but since an indeterminate weight is sifted and picked from the
slag, it is probable that the utilization of the materials is more
perfect than the above percentages. However, this seems to
be the part of the old Deville process least improved upon in
these new works, for there seems to be plenty of room for im-
provement in perfecting the utilization of materials, especially
in regard to loss of sodium by volatilization, which undoubt-
edly takes place and which can possibly be altogether pre-
vented.
The above description, written in 1890, was followed only
one year later by the closing of this splendid works. The very
lowest point to which the Deville-Castner process could reduce
the cost of producing aluminium was between 4 and S shillings
per pound ; and when the metal was put on the market by users
of the electrolytic process at $1.50 per pound, in 1891, there
was nothing left for the sodium process except to give up the
business. The company, however, continues to run the works,
making and selling large quantities of sodium.
i8
CHAPTER X.
REDUCTION OF ALUMINIUM COMPOUNDS BY MEANS OF
POTASSIUM OR SODIUM {Continued).
II.
Methods based on the reduction of cryolite.
These can be most conveniently presented in chronological
order.
Rose's Experiments (1855).
We will here give H. Rose's entire paper, as an account of
this eminent chemist's investigations written out by himself
with great detail, describing failures as well as successes,
cannot but be of value to all interested in the production of
aluminium:*
" Since the discovery of aluminium by Wohler, Deville has
recently devised the means of procuring the metal in large, solid
masses, in which condition it exhibits properties with which we
were previously unacquainted in its more pulverulent form as
procured by Wohler's method. While, for instance, in the lat-
ter state it burns vividly to white earthy alumina on being ig-
nited, the fused globules may be heated to redness without
perceptibly oxidizing. These differences may be ascribed to
the greater amount of division on the one hand and of density
on the other. According to Deville, however, Wohler's metal
contains platinum, by which he explains its difficulty of fusion,
although it affords white alumina by combustion. Upon the
publication of Deville's researches, I also tried to produce
aluminium by the decomposition of aluminium-sodium chloride
by means of sodium. I did not, however, obtain satisfactory
* Pogg. Annalen, Sept., 1855.
(274)
REDUCTION OF ALUMINIUM COMPOUNDS. 2/5
results. Moreover, Prof. Rammelsberg, who followed exactly
the method of Deville, obtained but a very small product, and
found it very difficult to prevent the cracking of the glass tube
in which the experiment was conducted, by the action of the
vapor of sodium on aluminium chloride. It appeared to me
that a great amount of time, trouble and expense, as well as
long practice, was necessary to obtain even small quantities of
this remarkable metal.
" The employment of aluminium chloride and its compounds
with alkali chlorides is particularly inconvenient, owing to their
volatility, deliquescence, and to the necessity of preventing all
access of air during their treatment with sodium. It very soon
occurred to me that it would be better to use the fluoride of
aluminium instead of the chloride ; or rather the combination
of the fluoride with alkaline fluorides, such as we know them
through the investigations of Berzelius, who pointed out the
strong affinity of aluminium fluoride for sodium fluoride and
potassium fluoride, and that the mineral occurring in nature
under the name of cryolite was a pure compound of aluminium
fluoride and sodium fluoride.
" This compound is as well fitted for the preparation of
aluminium by means of sodium as aluminium chloride or
aluminium-sodium chloride. Moreover, as cryolite is not vola-
tile, is readily reduced to the most minute state of division, is
free from water and does not attract moisture from the air, it
affords peculiar advantages over the above-mentioned com-
pounds. In fact, I succeeded with much less trouble in pre-
paring aluminium by exposing cryolite together with sodium
to a strong red heat in an iron crucible, than by using alu-
minium chloride and its compounds. But the scarcity of cryo-
lite prevented my pursuing the experiments. In consequence
of receiving, however, from Prof. Krantz, of Bonn, a consider-
able quantity of the purest cryolite at a very moderate price
($2 per kilo), I was enabled to renew the investigation.
" I was particularly stimulated by finding, most unexpect-
edly, that cryolite was to be obtained here in Berlin commer-
2/6 ALUMINIUM.
cially at an inconceivably low price. Prof. Krantz had already
informed me that cryolite occurred in commerce in bulk, but
could not learn where. Shortly after, M. Rudel, the manager
of the chemical works of H. Kunheim, gave me a sample of a
coarse white powder, large quantities of which were brought
from Greenland by way of Copenhagen to Stettin, under the
name of mineral soda, and at the price of $3 per centner.
Samples had been sent to the soap boilers, and a soda-lye
had been extracted from it by means of quicklime, especially
adapted to the preparation of many kinds of soap, probably from
its containing alumina. It is a fact, that powdered cryolite is
completely decomposed by quicklime and water. The fluoride
of lime formed contains no alumina, which is all dissolved by the
caustic soda solution ; and this, on its side, is free from fluor-
ine, or only contains a minute trace. I found this powder to
be of equal purity to that received from Prof. Krantz. It dis-
solved without residue in hydrochloric acid (in platinum ves-
sels) ; the solution evaporated to dryness with sulphuric acid,
and heated till excess of acid was dissipated, gave a residue
which dissolved completely in water, with the aid of a little
hydrochloric acid. From this solution, ammonia precipitated
a considerable quantity of alumina. The solution filtered from
the precipitate furnished, on evaporation, a residue of sulphate
of soda, free from potash. Moreover, the powder gave the
well-known reactions of fluorine in a marked degree. This
powder was cryolite of great purity : therefore the coarse pow-
der I first obtained was not the form in which it was originally
produced. It is now obtainable in Berlin in great masses ; for
the preparation of aluminium it must, however, be reduced to a
very fine powder.
" In my experiments on the preparatipn of aluminium, which
were performed in company with M. Weber, and with his most
zealous assistance, I made use of small iron crucibles, i ^
inches high and i^ inches upper diameter, which I had cast
here. In these I placed the finely divided cryolite between
thin layers of sodium, pressed it down tight, covered it with a
REDUCTION OF ALUMINIUM COMPOUNDS. 277
good layer of potassium chloride (KCl), and closed the cruc-
ible with a well-fitting porcelain cover. I found potassium
chloride the most advantageous flux to employ ; it has the low-
est specific gravity of any which could be used, an important
point when the slight density of the metal is taken into consid-
eration. It also increases the fusibility of the sodium fluoride.
I usually employed equal weights of cryolite and potassium
chloride, and for every five parts of cryolite two parts of so-
dium. The most fitting quantity for the crucible was found to
be ten grammes of powdered cryolite. The whole was raised
to a strong red heat by means of a gas-air blowpipe. It was
found most advantageous to maintain the heat for about half an
hour, and not longer, the crucible being kept closely covered
the whole time ; the contents were then found to be well fused.
When quite cold the melted mass is removed from the crucible
by means of a spatula ; this is facilitated by striking the outside
with a hammer. The crucible may be employed several times,
at last it is broken by the hammer blows. The melted mass is
treated with water, when at times only a very minute evolution
of hydrogen gas is observed, which has the same unpleasant
odor as the gas evolved during solution of iron in hydrochloric
acid. The carbon contained in this gas is derived from a very
slight trace of naphtha adhering to the sodium after drying it.
On account of the difficult solubility of sodium fluoride, the
mass is very slowly acted on by water, although the insolubility
is somewhat diminished by the presence of the potassium chlo-
ride. After twelve hours the mass is softened so far that it
may be removed from the liquid and broken down in a porce-
lain mortar. Large globules of aluminium are then discovered,
weighing from 0.3 to 0.4 or even 0.5 grammes, which may be
separated out. The smaller globules cannot well be separated
from the undecomposed cryolite and the alumina always pro-
duced by washing, owing to their being specifically lighter than
the latter. The whole is treated with nitric acid in the cold.
The alumina is not dissolved thereby, but the little globules
then first assume their true metallic lustre. They are dried and
278 ALUMINIUM.
rubbed on fine silk muslin ; the finely powdered, undecom-
posed cryolite and alumina pass through, while the globules
remain on the gauze. The mass should be treated in a plati-
num or silver vessel; a porcelain vessel would be powerfully
acted on by the sodium fluoride. The solution, after standing
till clear, may be evaporated to dryness in a platinum capsule,
in order to obtain the sodium fluoride, mixed however with
much potassium chloride. The small globules may be united
by fusion in a small well-covered porcelain crucible, under a
layer of potassium chloride. They cannot be united without a
flux. They cannot be united by mere fusion, like globules of
silver, for instance, for though they do not appear to oxidize
on ignition in the air, yet they become coated with a scarcely
perceptible film of oxide, which prevents their running together
into a mass. This fusion with potassium chloride is always at-
tended with a loss of aluminium. Buttons weighing 0.85
gramme lost, when so treated, 0.05 gramme. The potassium
chloride when dissolved in water left a small quantity of alu-
mina undissolved, but the solution contained none. Another
portion of the metal had undoubtedly decomposed the potas-
sium chloride ; and a portion of this salt and aluminium chlo-
ride must have been volatilized during fusion (other metals, as
copper and silver, behave in a similar manner — Pogg. Ixviii.
287). I therefore followed the instructions of Deville, and
melted the globules under a stratum of aluminium-sodium chlo-
ride in a covered porcelain crucible. The salt was melted first,
and 'then the globules of metal added to the melted mass.
There is no loss, or a very trifling one of a few milligrammes of
metal, by this proceeding. When the aluminium is fused
under potassium chloride its surface is not perfectly smooth,
but exhibits minute concavities ; with aluminium-sodium chlo-
ride this is not the case. The readiest method of preparing
the double chloride for this purpose is by placing a mixture of
alumina and carbon in a glass tube, as wide as possible, and
inside this a tube of less diameter, open at both ends, and con-
taining sodium chloride. If the spot where the mixture is
REDUCTION OF ALUMINIUM COMPOUNDS. 279
placed be very strongly heated, and that where the sodium
chloride is situated, more moderately, while a current of chlo-
rine is passed through the tube, the vapor of aluminium chlo-
lide is so eagerly absorbed by the sodium chloride that none
or at most a trace is deposited in any other part of the tube.
If the smaller tube be weighed before the operation, the
amount absorbed is readily determined. It is not uniformly
combined with the sodium chloride, for that part which is near-
est to the mixture of charcoal and alumina will be found to
have absorbed the most.
" I have varied in many ways the process for the preparation
of aluminium, but in the end have returned to the one just de-
scribed. I often placed the sodium in the bottom of the cruci-
ble, the powdered cryolite above it, and the potassium chloride
above all. On proceeding in this manner, it was observed that
much sodium was volatilzed, burning with a strong yellow
flame, which never occurred when it was cut into thin slices and
placed in alternate layers with the cryolite, in which case the
process goes on quietly. When the crucible begins to get red
hot, the temperature suddenly rises, owing to the commence-
ment of the decomposition of the compound ; no lowering of the
temperature should be allowed, but the heat should be steadily
maintained, not longer, however, than half an hour. By pro-
longing the process a loss would be sustained, owing to the
action of the potassium chloride on the aluminium. Nor does
the size of the globules increase on extending the time even to
two hours : this efifect can only be produced by obtaining the
highest possible temperature. If the process be stopped, how-
ever, after five or ten minutes of very strong heat, the produc-
tion is very small, as the metal has not had sufficient time
to conglomerate into globules, but is in a pulverulent form and
burns to alumina during the cooling of the crucible. No ad-
vantage is gained by mixing the cryolite with a portion of
chloride before placing it between the layers of sodium, neither
did I increase the production by using aluminium sodium
chloride to cover the mixture instead of potassium chloride. I
28o ALUMINIUM.
repeatedly employed decrepitated sodium chloride as a flux in the
absence of potassium chloride, without remarking any important
difference in the amount of metal produced, although a higher
temperature is in this case required. The operations may also
be conducted in refractory unglazed crucibles made of stone-
ware, and of the same dimensions, although they do not resist so
well the action of the sodium fluoride at any high heats, but fuse
in one or more places. The iron crucibles fuse, however,
when exposed to a very high temperature in a charcoal fire.
The product of metal was found to vary very much, even when
operating exactly in the manner recommended, and with the
same quantities of materials. I never succeeded in reducing the
whole amount of metal contained in the cryolite (which con-
tains 13 per cent, of aluminium). By operating on 10
grammes of cryolite, the quantity I always employed in the
small iron crucible, the most successful result was 0.8 grm. But
0.5 or even 0.4 grm. may be considered favorable ; many times
I obtained only 0.3 grm., or even less. These very different
results depend on various causes, more particularly, however,
on the degree of heat obtained. The greater the heat, the
greater the amount of large globules, and the less amount of
minutely divided metal to oxidize during the cooling of the
crucible. I succeeded once or twice in reducing nearly the
whole of the metal to one single button weighing 0.5 grm., at
a very high heat in a stoneware crucible. I could not always
obtain the same heat with the blowpipe, as it depended in some
degree on the pressure in the gasometer in the gas-works,
which varies at different hours of. the day. The following ex-
periment will show how great the loss of metal may be owing
to oxidation during the slow cooling of the crucible and its con-
tents: In a large iron crucible were placed 35 grms. of cryolite
in alternate layers with 14 grms. of sodium, and the whole cov-
ered with a thick stratum of potassium chloride. The crucible,
covered by a porcelain cover, was placed in a larger earthen
one also covered, and the whole exposed to a good heat in a
draft furnace for one hour, and cooled as slowly as possible.
REDUCTION OF ALUMINIUM COMPOUNDS. 28 1
The product in this case was remarkably small, for O.135 grm.
of aluminium was all that could be obtained in globules. The
differences in the amounts reduced depend also in some degree
on the more or less successful stratification of the sodium
with the powdered cryolite, as much of the latter sometimes
escapes decomposition. The greater the amount of sodium
employed, the less likely is this to be the case ; however, owing
to the great difference in their prices, I never employed more
than 4 grms. of sodium to 10 grms. of cryolite. In order to
avoid this loss by oxidation I tried another method of prepara-
tion : Twenty grms. of cryolite were heated intensely in a gun-
barrel in a current of hydrogen, and then the vapor of 8 grms.
of sodium passed over it. This was effected simply by placing
the sodium in a little iron tray in a part of a gun-barrel without
the fire, and pushing it forward when the cryolite had attained
a maximum temperature. The operation went on very well,
the whole being allowed to cool in a current of hydrogen.
After the treatment with water, in which the sodium fluoride
dissolved very slowly, I obtained a black powder consisting for
the most part of iron. Its solution in hydrochloric acid gave
small evidence of aluminium. The small amounts I obtained,
however, should not deter others from making these experi-
ments. These are the results of first experiments, on which I
have not been able to expend much time. Now that cryolite
can be procured at so moderate a price, and sodium by De-
ville's improvements will in future become so much cheaper, it
is in the power of every chemist to engage in the preparation of
aluminium, and I have no doubt that in a short time methods
M'ill be found affording a much more profitable result.
" To conclude, I am of opinion that cryolite is the best
adapted of all the compounds of aluminium for the preparation
of this metal. It deserves the preference over aluminium-sodium
chloride or aluminium chloride, and it might still be employed
with great advantage even if its price were to rise considerably.
The attempts at preparing aluminium direct from alumina have
as yet been unattended with success. Potassium and sodium
282 ALUMINIUM.
appear only to reduce metallic oxides when the potash and
soda produced are capable of forming compounds with a por-
tion of the oxide remaining as such. Pure potash and soda,
with whose properties we are very slightly acquainted, do not
appear to be formed in this case. Since, however, alumina
combines so readily with the alkalies to form aluminates, one
would be inclined to believe that the reduction of alumina by^
the alkali metals should succeed. But even were it possible to^
obtain the metal directly from alumina, it is very probable that
cryolite would long be preferred should it remain at a moderate
price, for it is furnished by nature in a rare state of purity, and
the aluminium is combined in it with sodium and fluorine only,
which exercise no prejudicial influence on the properties of the
metal, whereas alumina is rarely found in nature in a pure state
and in a dense, compact condition, and to prepare it on a large
scale, freeing it from those substances which would act injuri-
ously on the properties of the metal, would be attended with
great difficulty.
" The buttons of aluminium which I have prepared are so
malleable that they may be beaten and rolled out into the
finest foil without cracking on the edges. They have a strong
metallic lustre. Some small pieces, not globular, however,
were found in the bottom of the crucible, and occasionally ad-
hering to it, which cracked on being hammered, and were dif-
ferent in color and lustre from the others. They were evi-
dently not so pure as the greater number of globules, and con-
tained iron. On sawing through a large button weighing 3.8
grammes, it could readily be observed that the metal for abotit
half a line from the exterior was brittle, while in the interior it
was soft and malleable. Sometimes the interior of a globule
contained cavities. With Deville, I have occasionally observed
aluminium crystallized. A large button became striated and
crystalline on cooling. Deville believes he has observed reg-
ular octahedra, but does not state this positively. According
to my brother's examination, the crystals do not belong to any
of the regular forms. As I chanced on one occasion to attempt
REDUCTION OF ALUMINIUM COMPOUNDS. 283
the fusion of a large, flattened- out button of rather impure
aluminium, without a flux, I observed, before the heat was suffi-
cient to fuse the mass, small globules sweating out from the
surface. The impure metal being less fusible than pure metal,
the latter expands in fusing and comes to the surface."
Experiments of Percy and Dick (1855).
After the publication of Rose's results, widespread attention
was directed toward this field, and it was discovered that some
six months previously Dr. Percy, in England, had accomplished
almost similar results, and had even shown a specimen of the
metal to the Royal Institution, but with the singular fact of ex-
citing very little attention. These facts are stated at length in
the following paper written by Allan Dick, Esq., which ap-
peared in November, 1855, two months after the publication of
H. Rose's paper: — *
" In the last number of this magazine was the translation of a
paper by H. Rose, of Berlin, describing a method of preparing
aluminium from cryolite. Previously, at the suggestion of Dr.
Percy, I had made some experiments on the same subject in
the metallurgical laboratory of the School of Mines ; and as the
results obtained agree very closely with those of Mr. Rose, it
may be interesting to give a short account of them now, though
no detailed description was published at the time, a small piece
of metal prepared from cryolite having simply been shown at
the weekly meeting of the Royal Institution, March 30, 1855,
accompanied by a few words of explanation by Faraday.
" Shortly after the publication of Mr. Deville's process for
preparing aluminium from aluminium chloride, I tried along
with Mr. Smith to make a specimen of the metal, but we found
it much more difficult to do than Deville's paper had led us to
anticipate, and had to remain contented with a much smaller
piece of metal than we had hoped to obtain. It is, however,
undoubtedly only a matter of time, skill, and expense to join
* Phil. Mag., Nov. 1855.
284 ALUMINIUM.
successful practice with the details given by Deville. Whilst
making these experiments, Dr. Percy had often requested us to
try whether cryolite could be used instead of the chlorides, but
some time elapsed before we could obtain a specimen of the
mineral. The first experiments were made in glass tubes
sealed at one end, into which alternate layers of finely powdered
cryolite and sodium cut into small pieces were introduced, and
covered in some instances with a layer of cryolite, in others by
sodium chloride. The tube was then heated over a gas blow-
pipe for a few minutes till decomposition had taken place, and
the product was melted. When cold, on breaking the tube, it
was found that the mass was full of small globules of aluminium,
but owing to the specific gravity of the metal and flux being
nearly alike, the globules had not collected into a button
at the bottom. To effect this, long-continued heat would be
required, which cannot be given in glass tubes owing to the
powerful action of the melted fluoride on them. To obviate
this difficulty, a platinum crucible was lined with magnesia
by ramming it in hard and subsequently cutting out all but
a lining. In this, alternate layers of cryolite and sodium were
placed, with a thickish layer of cryolite on top. The cruci-
ble was covered with a tight-fitting lid, and heated to redness
for about half an hour over a gas blowpipe. When cold it was
placed in water, and after soaking for some time the contents
were dug out, gently crushed in a mortar, and washed by de-
cantation. Two or three globules of aluminium, tolerably large
considering the size of the experiment, were obtained, along
with a large number of very small ones. The larger ones were
melted together under potassium chloride. Some experiments
made in iron crucibles were not attended with the same success
as those of Rose : no globules of any considerable size re-
mained in the melted fluorides ; the metal seemed to alloy on
the sides of the crucible, which acquired a color like zinc. It
is possible that this difference may have arisen from using a
higher temperature than Rose, as we made these experiments
in a furnace, not over the blowpipe. Porcelain and clay cru-
REDUCTION OF ALUMINIUM COMPOUNDS. 285
cibles were also tried, but laid aside after a few experiments,
owing to the action of the fluorides upon them, which in most
cases was sufificient to perforate them completely."
Deville's Methods (1856-8).
* " I have repeated and confirmed all the experiments of Dr.
Percy and H. Rose, using the specimens of cryolite which I
obtained from London through the kindness of MM. Rose and
Hofmann. I have, furthermore, reduced cryolite mixed with
sodium chloride by the battery, and I believe that this will be
an excellent method of covering with aluminium all the other
metals, copper in particular. Anyhow, its fusibility is consid-
erably increased by mixing it with aluminium-sodium chloride.
Cryolite is a double fluoride of aluminium and sodium, con-
taining 13 per cent, of aluminium and having the formula
AlFj.sNaF. I have verified these facts myself by many
analyses.
" In reducing the cryolite I placed the finely pulverized mix-
ture of cryolite and sodium chloride in alternate layers with
sodium in a porcelain crucible. The uppermost layer is of
pure cryolite, covered with salt. The mixture is heated just to
complete fusion, and after stirring with a pipe-stem, is let cool.
On breaking the crucible, the aluminium is often found united
in large globules, easy to separate from the mass. The metal
always contains silicon, which increases the depth of its natural
blue tint and hinders the whitening of metal by nitric acid, be-
cause of the insolubility of the silicon in that acid. M. Rose's
metal is very ferruginous. I have verified all M. Rose's ob-
servations, and I agree with him concerning the return of
metal, which I have always found very small. There are al-
ways produced in these operations brilliant flames, which are
observed in the scoria floating on the aluminium, and which
are due to the gas burning and exhaling a very marked odor
of phosphorus. In fact, phosphoric acid exists in cryolite, as
* Ann. de Chim. et de Phys. [3], xlvi. 451.
286 ALUMINIUM.
one may find by treating a solution of the mineral in sulphuric
acid with molybdate of ammonia, according to H. Rose's re-
action.
" M. Rose has recommended iron vessels for this operation,
because of the rapidity with which alkaline fluorides attack
earthen crucibles and so introduce considerable silicon into the
metal. Unfortunately, these iron crucibles introduce iron into
the metal. This is an evil inherent in this method, at least in
the present state of the industry. The inconveniences of this
method result in part from the high temperature required to
complete the operation, and from the crucible being in direct
contact with the fire, by which its sides are heated hotter than
the metal in the crucible. The metal itself, placed in the lower
part of the fire, is hotter than the slag. This, according to my
observations, is an essentially injurious condition. The slag
ought to be cool, the metal still less heated, and the sides of
the vessel where the fusion occurs ought to be as cold as pos-
sible. The yield from cryolite, according to Rose's and my own
observations, is also very small. M. Rose obtained from lo of
cryolite and 4 of sodium about 0.5 of aluminium. This is due
to the affinity of fluorine for aluminium, which must be very
strong not only with relation to its affinity for sodium, but even
for calcium, and this affinity appears to increase with the tem-
perature, as was found in my laboratory. Cryolite is most
convenient to employ as a flux to add to the mixture which is
fused, especially when operating on a small scale.
"The argument which decided the company at Nanterre not
to adopt the method of manufacture exclusively from cryolite
was the report of M. de Chancourtois, mining engineer, who
had just returned from a voyage to Greenland. According to
the verbal statements of this gentleman, the gite at Evigtok is
accessible only during a very short interval of time each year,
and, because of the ice fields, can only be reached then by a
steamboat. The workmen sent from Europe to blast and load
up the rock have scarcely one or two months of work possible.
The local workmen remain almost a whole year deprived of all
REDUCTION OF ALUMINIUM COMPOUNDS. 287
communication with the rest of the world, without fresh provi-
sions or fuel other than that brought from Europe in the short
interval that navigation is open. The deposit itself, which is
scarcely above sea-level, can be easily worked with open roof,
but the neighborhood of the sea in direct contact with the vein,
the unorganized manner of working, and the lack of care in
keeping separate the metalliferous portions of the ore — all com-
bine to render the mineral very costly, and further developments
underground almost impossible.
" It is therefore fortunate that cryolite is not indispensable,
for no one would wish to establish an industry based on the
employment of a material which is of such uncertain supply."
Tissier Bros.' Method (1857).
The process adopted in the works at Amfreville, near Rouen,
directed by Tissier Bros., is essentially that described by Percy
and Rose. The method of operating is given by the Tissier
Bros, themselves in their book as follows :
"After having finely powdered the cryolite, it is mixed with
a certain quantity of sodium chloride (sea salt), then placed be-
tweeen layers of sodium used in the proportions given by M.
Rose, in large refractory crucibles. These are heated either in
a reverberatory furnace or in a wind furnace capable of giving
a temperature high enough to melt the fluoride of sodium pro-
duced by the reaction. As the sodium fluoride requires a
pretty high temperature to fuse it, the heat will necessarily be
higher than that required in the reduction of the double
chloride of aluminium and sodium. When the contents of the
crucible are melted, so as to be quite liquid, the fusion is poured
into cast-iron pots, at the bottom of which the aluminium col-
lects in one or several lumps."
Tissier Bros, claimed the following advantages for the use of
cryolite :
" Cryolite comes to us of a purity difficult to obtain with the
double chloride of aluminium and sodium, to which it exactly
corresponds ; and since, thanks to the perfection we have at-
288 ALUMINIUM.
tained in using it, the return of aluminium is exactly correspon-
dent to the amount of sodium used in reduction, it is easily seen
what immense advantages result from its employment. The
double chloride deteriorates in the air, it gives rise in the works
to vapors more or less deleterious and corrosive, and its price
is always high. Cryolite can be imported into France at a
price so low that we have utilized it economically for making
commercial carbonate of soda ; it remains unaltered in the air,
emits no deleterious vapors, and its management is much more
easy than that of the double chloride. Moreover, on compar-
ing the residues of the two methods of reduction, the manufac-
ture from double chloride leaves sodium chloride, almost with-
out value, while the manufacture from cryolite leaves sodium
fluoride, which may be converted for almost nothing into
caustic soda or carbonate, and so completely cancels the cost
of the cryolite from the cost of aluminium. The most serious
objection which can be made to using cryolite is that the
sources of the mineral being up to the present very limited, the
future prospect of aluminium Hes necessarily in the utilization
of clays and their transformation into aluminium chloride ; but,
admitting that other sources of cryolite may not be discov-
ered hereafter, the abundance of those which exist in Greenland
will for a long time to come give this mineral the preference in
the manufacture of aluminium."
The most serious difhculty which this process had to meet,
and which it could not overcome, was the high content of sili-
con in the metal produced. A specimen of their aluminium
made in 1859 contained 4.4 per cent, of silicon alone (see p.
54, Analysis 7). The firm at Rouen went out of business about
1863 or 1865 — I am unable to give the exact date. From that
time until quite recently, it has been considered that the best
use of cryolite is as a flux in the preparation of aluminium from
aluminium-sodium chloride, in which case the slag is not sodium
fluoride, but aluminium fluoride, which acts but slightly on the
containing vessel.
REDUCTION OF ALUMINIUM COMPOUNDS. 289
Wohler' s Modifications (1856).
Wohler suggested the following modifications of Deville's
process of reducing cryolite in crucibles, by means of which
the reduction can be performed in an earthen crucible without
the metal produced taking up silicon.
*"The finely pulverized cryolite is mixed with an equal
weight of a flux containing 7 parts sodium chloride to 9 parts
potassium chloride. This mixture is then placed in alternate
layers with sodium in the crucible, 50 parts of the mixture to
10 of sodium, and heated gradually just to its fusing point.
The metal thus obtained is free from silicon, but only one-third
of the aluminium in the cryolite is obtained." In spite of the
small yield, this method was used for some time by Tissier
Bros.
Gerhard's Furnace (1858).
This furnace was devised for the reduction of aluminium
either from aluminium-sodium chloride or from cryolite, the
object being to prevent loss of sodium by ignition. It was in-
vented and patented by W. F. Gerhard. | " It consists of a
reverberatory furnace having two hearths, or of two crucibles,
or of two reverberatory furnaces, placed one above the other
and communicating by an iron pipe. In the lower is placed a
mixture of sodium with the aluminium compound, and in the
upper a stratum of sodium chloride, or of a mixture of this
salt and cryolite, or of the slag obtained in a previous ope-
ration. This charge, when melted, is made to run into the
lower furnace in quantity sufficient to completely cover the
mixture contained therein, and so to protect it from the air.
The mixture thus covered is reduced as by the usual operation."
Whether a furnace was ever put up and operated on this
principle, the author cannot say. It is possible that it may
have been used in the English manufactory started in 1859
at Battersea near London. (See p. 18.)
* Ann. der Chem. und Pharm. 99,255.
t Eng. Pat., 1858, No. 2247.
19
290 ALUMINIUM.
Thompson and White's Patent (1887).
* J. B. Thompson and W. White recommend heating a mix-
ture of 3 parts sodium and 4 parts cryolite to 100°, whereby
the sodium becomes pasty and the whole can be well kneaded
together with an iron spatula. When cold, 4 parts of alumin-
ium chloride are added, and the mixture put into a hopper on
top of a well-heated reverberatory furnace, with a cup-shaped
hearth. The charge is dropped into the furnace and the
reaction takes place at once. To produce alloys, this patent
claims 16 parts of cryolite are mixed with 5 parts of sodium,
the metal added before reduction and the mixture treated as
above, by which means explosions are avoided. The pre-
liminary heating to 100° is effected in a jacketed cast-iron pot
connected with a circulating boiler.
Hampe's Experiment (1888).
t Dr. W. Hampe failed to produce aluminium bronze by treat-
ing cryolite with sodium in the presence of copper. A mixture of
Finely divided copper 44 grammes,
Sodium, in small pieces, 15 "
Finely powdered cryolite 100 "
was melted rapidly in a carbon-lined crucible. There were no
sounds given out such as usually accompany other reductions
by sodium, but much sodium vapor was given off. The copper
button contained only traces of aluminium.
Netto's Process (1887).
Dr. Curt Netto, of Dresden, patented in England and Ger-
many, in spring and autumn of 1887, processes for producing
sodium and potassium and methods of using them in producing
aluminium. His experiments were made in conjunction with
Dr. Salomon, of Essen, and the fact that the experimental ap-
* English patent 8427, June 11, 1887.
tChemiker Zeitung, (Cothen), xii, p. 391.
REDUCTION OF ALUMINIUM COMPOUNDS. 29 1
paratus was put up in Krupp's large steel works at Essen gave
rise to reports that the latter had taken up the manufacture of
aluminium by some new and very successful process, intending
to use it for alloys in making cannon. *
In the latter part of 1888 was formed the Alliance Aluminium
Co. of London, England, capitalized at ;£'5oo,ooo, purposing to
manufacture sodium and aluminium, and owning the English,
French, German, and Belgian patents of Dr. Netto for the pro-
duction of those metals, also the processes of a Mr. Cunning-
ham for the same purpose, also a process for the production of
artificial cryolite by the regeneration of slag (provisionally pro-
tected by its inventor, Mr. Forster, of the Lonesome Chemical
Works, Streatham), and, lastly, a process invented by Drs.
Netto and Salomon by which aluminium can be raised to the
highest standards of purity on a commercial scale. A note
accompanying the above announcement stated that the exhaust-
ive experiments made at Essen had satisfactorily demonstrated
the practicability of the processes, and that the company had
already contracted with the cryolite mines of Greenland for all
the cryolite they would need.
In June, i888,t the Alliance Aluminium Company had in
operation a small aluminium plant at King's Head Yard, Lon-
don, E. C, and when the process was in continuous opera-
tion the cost of the metal was set down at 6 shillings per
pound. It is probable that the metal exhibited in the Paris
Exposition of 1889 was produced at this place.
In April, 1889,! ten acres of ground had been leased at
Hepburn on which to produce sodium by Capt. Cunningham's
process. The sodium produced was to be sent to Wallsend to
be used by the Alliance Aluminium Company, who were erect-
ing a large works at that place.
As for Capt. Cunningham's sodium processes, they are ap-
parently identical with Dr. Netto's. Cunningham's aluminium
♦American Register, Paris, August, 1888.
t Engineering, June i, 1888.
X E. and M. J., April 27, 1889.
292
ALUMINIUM.
process* consists in melting the sodium to be used with lead,
in order to facihtate the submerging of the sodium under the
molten aluminium salt. The alloy is cast into bars and added
piece by piece to the bath of molten aluminium salt on the
hearth of a reverberatory furnace. After the reaction the mix-
ture separates by specific gravity into lead, containing a little
aluminium, and aluminium containing a little lead, the slag
floating on top of all. Aluminium is known to have so small an
attraction for lead that this result becomes possible.
Fig. 26.
Dr. Netto recommends several processes, the one used at
London being the following: — |
One hundred parts of cryolite and 30 to 100 parts of sintered
sodium chloride are melted at a red heat in a well-covered clay
crucible. (Another arrangement, and apparently a better, is to
melt this mixture on the hearth of a reverberatory furnace and
tap it into a deep, conical ladle, in which the succeeding opera-
tions proceed as about to be described. See Fig. 26.) As soon
as the bath is well fused, 35 parts of sodium at the end of a rod, and
* English Patent, 16727, Dec. 5, 1887.
t German Patent (D. R. P.), 45198, March 26, 1887.
REDUCTION OF ALUMINIUM COMPOUNDS. 293
covered over by a perforated concave plate is pushed quickly
down to the bottom of the crucible. The plate mentioned fits
across the whole section of the crucible at its lower part, so that
the fusible, easily volatile sodium, being vaporized, is divided into
very fine streams as it passes upwards through the bath, and is
all utilized before it reaches the surface. In this way the re-
action is almost instantaneous, and the contents can be poured
out at once into iron pots, where, on cooling, the metal is found
as a large lump at the bottom.
It is further observed that to avoid explosions on introducing
the sodium it should have in it no cavities which might contain
moisture or hydrocarbons. In consequence of the reaction be-
ing over so quickly, and the heat set free in the reduction, the
syrupy fusion becomes thin as water, and the aluminium dis-
seminated through the mass collects together completely, so
that the slag contains no particles visible to the eye. Since the
reduction, pouring, and cooling take place so quickly, the alu-
minium is not noticeably redissolved by the bath, thus insuring
a high return of metal. By using 35 parts of sodium to 100
parts of cryolite, 10 parts of aluminium are obtained. Since
the cryolite contains 13 per cent, of aluminium, the return is
yy per cent, of the amount of metal in the cryolite; since 35
parts of sodium should theoretically displace 14 parts of alu-
minium, the return is 71 per cent, of the amount which the
sodium should produce. Dr. Netto claims that this is double
the return formerly obtained from cryolite. The metal pro-
duced is said to be from 98.5 to 99 per cent. pure.
The apparatus erected at Krupp's works at Essen, which was
described by the newspapers as similar to a Bessemer converter,
was constructed and operated as follows : A large iron cylinder
is pivoted at the centre in a manner similar to a Bessemer con-
verter. Passing through the centre of the cylinder, longitudi-
nally, is a large iron tube in which generator gas is burnt to
heat the vessel.. To heat it up, it is placed erect, connection
made with the gas-main, while a hood above connects with the
chimney. On top of the cylinder, a close valve communicates
294 ALUMINIUM.
with the interior, for charging, and at the other end is a tap-
hole. The charge of cryoHte being put in, the flame is passed
through the central tube until the mineral is well fused. Then
soHd or melted sodium is passed in at the top, the valve is
screwed tight, the gas shut off, and the whole cylinder is rotated
several times until reduction is complete, when it is brought
upright, the tap-hole opened and slag and metal tapped into a
deep iron pot, where they separate and cool. Aluminium thus
made could not but contain much iron, even up to 14 per cent.,
it is said, which would prevent its use for any purpose ex-
cept alloying with iron. To procure pure aluminium, the ves-
sel would have to be properly fettled.
Dr. Netto also devised an arrangement similar to Heaton's
apparatus for making steel. It consisted of a large, well-lined
vessel on trunnions, the bottom of which was filled to a certain
depth with sodium, then a perforated aluminium plate placed
like a false bottom over it. On pouring molten cryolite into
the vessel, the aluminium plate prevented the sodium from rising
en masse to the surface of the cryolite. After the reaction was
over, the vessel was tilted and the slag and metal poured out
into iron pots.
The modification of the crucible method appears to have
been the most feasible of Netto's processes, and was probably
that used at Wallsend by the Alliance Aluminium Com-
pany. Outside estimates of the cost of aluminium to this com-
pany placed it at $1.50 to $2 per pound. They were selling in
the latter part of 1889 at 11, 13, and 15 shillings per pound,
according to quality, but were forced out of the business by the
electrolytic processes in 189 1.
Grabau's Process (1887).
There is only one patentee claiming particularly the reduc-
tion of aluminium fluoride by sodium — Ludwig Grabau, of
Hannover, Germany. His patents on this subject are im-
mediately preceded by others on a method of producing the
aluminium fluoride cheaply, which are described on p. 171, and
REDUCTION OF ALUMINIUM COMPOUNDS. 295
the inventor has patented a process which will furnish him with
cheap sodium. Mr. Alexander Siemens is authority for the
statement that a plant was in operation in the spring of 1889,
in Hannover, producing aluminium by this process on a com-
mercial scale. The principal object of Mr. Grabau's endeavors
has been to produce metal of a very high degree of purity. To
this end every precaution is taken to procure pure materials
and to prevent contamination during reduction. We will quote
from a paper written by Mr. Grabau* and also from his speci-
fications,f the following explanation of the process :
" The purifying of impure aluminium is accompanied by so
many difficulties that it appears almost impossible. It is there-
fore of the greatest importance to so conduct the operation that
every impurity is excluded from the start. Molten aluminium
compounds, whether a flux is added or not, attack any kind of
refractory vessels and become siliceous if these vessels are made
of chamotte or like materials, or if made of iron they become
ferruginous. These impurities are reduced in the further pro-
cesses and pass immediately into the aluminium as iron, silicon,
etc. Evidently the case is altered if an aluminium compound
which is infusible can be used advantageously. Aluminium
fluoride is infusible and also retains its pulverized condition
when heated up to the temperature needed for its use ; it can
therefore be heated in a vessel of any kind of refractory mater-
ial, or even in a metallic retort, without danger of taking up any
impurity.
" Further, it is necessary for succeeding in producing alu-
minium that the reduced metal thall unite to a large body after
the reduction. For this purpose all previous processes use
fluxes, and usually cryolite. But cryolite is impure, and there-
fore here is a source of many of the impurities in commercial
aluminium. Dr. K. Kraut, of Hannover, has observed that,
according to the recent analyses of Fresenius and Hintz, com-
* Zeitschrift fur angewandte, Chemie, 1889, vol. 6.
t German Pat. (D. R. P.) 47°3'. Nov. 15, 1887. English Pat. 15593, Nov. 14,
1887. U. S. Patents 386704, July 24, l888; and 400449, April 2, 1889.
296 ALUMINIUM.
mercial cryolite contains 0.80 to 1.39 per cent, of silicon, and
o.ii to 0.88 per cent, of iron, and that these impurities inter-
penetrate the mineral in such a manner as to be often only vis-
ible under the microscope, and therefore totally impossible of
removal by mechanical means. It is thus seen that the avoid-
ance of the use of any Rux is of great importance as far as
producing pure metal is concerned, as well as from an eco-
nomic standpoint.
" By the following process it is also possible to reduce alu-
minium fluoride by ?odium without the vessel in which reduc-
tion takes place being attacked either by the aluminium-sodium
fluoride formed or by the reduced aluminium. For this pur-
pose the aluminium fluoride and sodium are brought together
in such proportions that after the reaction there is still suffi-
cient aluminium fluoride present to form with the sodium flu-
oride resulting from the reaction a compound having the com-
position of cryolite. The reaction, therefore, will be
2AlF3-h3Na=Al-l-AlF3.3NaF.
" Using these proportions, the aluminium fluoride must be
previously warmed up to about 600° C, in order that when it is
showered down upon the melted sodium the reaction may com-
mence without further application of heat. The aluminium
fluoride remains granular at this temperature and therefore re-
mains on top of the melted sodium, like saw-dust or meal upon
water, and under its protection the reaction proceeds from
below upwards — an important advantage over the usual method
of pouring molten aluminium compounds on to sodium, in
which the lighter sodium floats to the top and burns to waste.
If solid sodium is used in my process the aluminium fluoride
must be somewhat hotter on being poured into the reduction
vessel, or about 700° C. For carrying out the process the re-
duction vessel must be artificially cooled, so as to form a lining
by chilling some of the aluminium-sodium fluoride formed by
the reaction, on the inner walls. This lining is in no wise
further attacked by the contents of the vessel, nor can it evi-
dently supply to them any impurity.
REDUCTION OF ALUMINIUM COMPOUNDS.
297
Fig. 27.
298 ALUMINIUM.
"The furnace A (Fig. 27) with grate B and chimney C,
serves for heating the iron retorts D and E, which are coated
with chamotte and protected from the direct action of the flame
by brick work. The vessel D serves for heating the aluminium
fluoride, and is provided with a damper or sliding valve be-
neath. The sodium is melted in E, and can be emptied out by
turning the cock k. The water-jacketed reduction vessel is
mounted on trunnions to facilitate emptying it. The retorts
are first heated dark red-hot, and D is filled with the conven-
ient quantity of aluminium fluoride. When this has become
red hot, as is shown by a small quantity of white vapor is-
suing from it, the required quantity of sodium is put into E.
This melts very quickly, and is then immediately run into the
reduction vessel by opening the stop-cock k. As soon as it is
transferred, the slide at the base of the retort D is pulled out
and the whole quantitity of aluminium fluoride falls at once
upon the sodium, and the reaction begins. As before re-
marked, the granular form of the aluminium fluoride keeps it
on top of the sodium, so that the latter is completely covered
during the whole reaction. This prevents almost altogether
any waste of sodium by volatilization. Dr. K. Kraut testifies
to an operation which he witnessed in which the return showed
83 per cent, of the sodium to have been utilized. An efficiency
in this respect of over 90 per cent, has been occasionally
reached, while the average is 80 to 90. Ad. Wurtz states that
the average for several years' working of the Deville process
showed only 74.3 per cent, of the quantity of aluminium pro-
duced which the sodium used could have given.
"During the reaction a very high temperature is developed,
so that the cryolite formed becomes very fluid, but is chilled
against the sides of the vessel to a thickness of a centimetre or
more. This crust is a poor conductor of heat, and is neither
attacked by the fluid cryolite nor by the aluminium. In con-
sequence of the great fluidity of the bath, it is possible for the
aluminium to unite into a body without the use of any flux,
The reaction being over, which is accomplished with the above
REDUCTION OF ALUMINIUM COMPOUNDS. 299
proportions of materials in a few seconds, and the vessel hav-
ing been shaken briskly backwards and forwards a few times to
facilitate the settling of the aluminium, the whole is turned on
the trunnions and emptied into a water-jacketed iron pot, where
it cools. The crust of cryolite inside the reduction vessel is
left there, and the apparatus is ready for another operation."
M. Grabau, in a private communication to the author, sums
up the advantages of his process, including the production of
the aluminium fluoride, as follows : —
1. The process is not dependent on natural cryolite, which is
expensive, impure and not easily purified.
2. The raw material — aluminium sulphate — can be procured
in large quantities and of perfect purity.
3. The aluminium fluoride is produced by a wet process,
which offers no difficulties to production on a large scale.
4. The fluorspar may be completely freed from foreign
metals by washing with dilute acid ; any silica present is not
injurious, as it remains undissolved in the residue during the
reactions.
5. The cryolite formed in each reduction contains no impur-
ities, and an excess of it is produced which can be sold.
6. The reduction of aluminium fluoride by my method gives
a utilization of 80 to 90 per cent, of the sodium used, which is
much more than can be obtained by other processes.
7. Aluminium fluoride is infusible, and can therefore be
heated in a vessel of any refractory material without taking up
any impurities. It is also unchanged in the air, and can be
kept unsealed for any length of time without deteriorating in
the least.
8. No flux has to be added for reduction, the use of impure
flux being a frequent cause of impurity of the metal.
In point of fact, M. Grabau has succeeded in producing sev-
eral hundred pounds of aluminium averaging over 99^ per
cent. pure. Dr. Kraut reports an analysis of an average speci-
men with 99.62 per cent, of aluminium (see Analysis 20, p. 54),
and metal has been made as pure as 99.8 per cent., a piece of
300 ALUMINIUM.
which has been kindly forwarded the author by M. Grabau, and
I freely admit it to be as fine a specimen of aluminium as I have
ever seen. Metal of such purity and fineness can only be made
by the electrolytic processes at considerable expense over ordi-
nary best commercial metal, since they must use chemically pure
alumina and extra precautions as to the purity of the electrodes.
It therefore appears possible that M. Grabau may yet be able
to manufacture and sell this extra quality aluminium, if he can
bring its price anywhere near that of the electrolytic aluminium.
The Grabau Aluminium Werke, Trotha, Germany, operates the
Grabau processes, and does a business in manufacturing and
selling sodium.
CHAPTER XI.
REDUCTION OF ALUMINIUM COMPOUNDS BY THE USE OF
ELECTRICITY.
As preliminary to the presentation of the various electrolytic
methods which have been proposed or , used, it may be profit-
able to review briefly the principles of electro-metallurgy as
they apply to the decomposition of aluminium compounds.
Some additional observations have been already included in
Chapter VIII.
The atomic weight of aluminium being 27, its chemical
equivalent, or the weight of it equal in consbining power to one
part of hydrogen, is 9. Therefore a current of quantity sufiS-
cient to liberate i part of hydrogen in a certain time would
produce 9 parts of aluminium in the same time, according to
the fundamental law of electric decomposition. It has been
determined that a current of i ampere acting for one second,
liberates 0.00001035 grammes of hydrogen; therefore it will
produce or set free from combination in the same time,
0.00009315 grammes of aluminium. This is the electro-chemical
equivalent of aluminium. Now, from thermo-chemical data we
know that the amount of energy required to set free a certain
weight of aluminium will vary with the compound from which
it is produced ; but the above equivalent is independent of the
compound decomposed, therefore there must be some varying
factor connected with the quantity of the current to account
for the different amounts of work which the current does in
decomposing diflferent compounds of the same element. This
is exactly in accordance with the principles of the mechanical
or thermal equivalent of the electric current, for the statement
" a current of one ampere," while it expresses a definite quan-
(301)
302 ALUMINIUM.
tity of electricity, yet carries no idea of the energy represented
by that current; we must know against what resistance or with
what electro- motive force that quantity is moved, and then we
can calculate its mechanical equivalent. Now, a current of i
ampere flowing against a resistance of i ohm, or in other
words, with a moving force or intensity of i volt, represents a
quantity of energy in one second equal to 0.00024 calories of
heat or to O.I kilogrammetre of work, and is therefore nearly
^ijf of a horse power. Therefore we can calculate the theoreti-
cal intensity of current necessary to overcome the affinities of
any aluminium compound for which we know the appropriate
thermal data. For instance, when aluminium forms its chlo-
ride (see p. 228) ^ — — — =5,960 calories are developed per
54
kilo of aluminium combining ; consequently the liberating of
0.00009315 grammes of aluminium (its electro-chemical equiva-
lent), requires the expenditure of an amount of energy equal to
0.00009315 X 5.960 = 0.000555 calories. Since a current of
I ampere at an intensity of i volt represents only 0.00024 cal-
ories, the intensity of current necessary to decompose alumin-
ium chloride is theoretically — '- — ^= 2.3 volts. In a simi-
0.00024
lar manner we can calculate that to decompose alumina would
, . ^. , , 391600 0.00000009315
require an electro-motive force of x Z^-^ =
54 0.00024
2.8 volts. These data would apply only to the substances
named, in a fused anhydrous state ; with hydrated aluminium
chloride in solution, a far. greater electro-motive force would be
necessary. If we had the thermal data we could also calculate
the intensity of current necessary to decompose the sulphate,
nitrate, acetate, etc., in aqueous solution; but failing these, we
can reason from analogy that it would be several volts in each
case.
It must be noted also, that these heats of combination are
those observed at ordinary temperatures. To find the voltage
required at high temperatures we must make allowance for the
REDUCTION OF ALUMINIUM COMPOUNDS. 303
weakening of the affinities, that is, for the decrease in heat of
combination as the temperature rises. When the rate of this
decrease is known, the true voltage required at any temperature
can be calculated. Often the operation is reversed ; that is, the
minimum electro-motive force required to effect decomposition
is accurately measured at different temperatures, and from
these data the variation in the heat of formation with the tem-
perature can be calculated by reversing the above calculations.
For example of this see p. 239.
To utilize such calculations, we must bear in mind exactly
what they represent. To decompose fused aluminium chloride,
for instance, not only must the current possess an intensity of
2.3 volts, but it must in addition have power enough above this
to overcome the transfer resistance of the electrolyte ; i. e., to
force the current through the bath from one pole to the other.
So, then, 2.3 volts would be the absolute minimum of intensity
which would produce decomposition, and the actual intensity
practically required would be greater than this, varying with
the distance of the poles apart and the temperature of the
bath as far as it affects the conducting power of the electrolyte.
From this it would immediately follow that if the substance to
be decomposed is an absolute non-conductor of electricity, no
intensity of current will be able to decompose it. If, on the
other hand, the substance is a conductor and the poles are
within reasonable distance, a current of a certain intensity will
always produce decomposition. The objection is immediately
made that in most cases no metal is obtained at all, which is
true not because none is produced, but because it is often dis-
solved by secondary actions as quickly as it is produced. I
need but refer to the historic explanation of the decomposition
of caustic soda in aqueous solution, although we have cases
hardly parallel to this in which the electrolyte itself dissolves
the separated metal.
How about the case of aqueous solutions ? Water requires a
minimum electro-motive force of 1.5 volts to decompose it,
and hence a prominent electrician remarked of a compound
304 ALUMINIUM.
which theoretically required over 2 volts that its decomposition
in aqueous solution would involve the decomposition of the
water and therefore was impossible. This remark is only partly
true ; for caustic soda requres over 2 volts, yet if mercury is
present to absorb the sodium as it is set free and protect it from
the water, we will obtain sodium, while the water is decomposed
at the same time. The truth seems to be that if two substances
are present which require different electro-motive forces to de-
compose them, a current of a certain intensity will decompose
the one requiring the least force, without affecting the other at
all; but, if it is of an intensity sufficient to decompose the
higher compound, then the current will be divided in some ratio
between the two, decomposing them both. This theory would
render theoretically possible the decomposition of aluminium
salts in aqueous solution, with a waste of power proportional to
the amount of water decomposed at the same time ; but
whether any aluminium would be obtained would be contingent
on the secondary action of the water on the aluminium. Pure
aluminium in mass is not acted upon by water, but the foil is
rapidly eaten away by boihng water. The state of division of
the metal, then, determines the action of water on it, and it is
altogether probable that the reason why aluminium is not easily
deposited from aqueous solution is that, like sodium, it is
attacked as soon as isolated, the acidity of the solution convert-
ing the hydrate formed back into the salt, or else simply the
hydrate remaining. Unfortunately, mercury does not exercise
the same function with aluminium as with sodium, for water at-
tacks its amalgam with aluminium, and so destroys the metal.
It is possible that if some analogous solvent could be found which
protected the aluminium from the action of water, the deposi-
tion from aqueous solution could be performed quite easily.
The electro-deposition of a metal using a soluble anode is
entirely a different affair. In this case, while the salt in solu-
tion is decomposed, yet it is immediately regenerated by the
acid radical set free dissolving from the anode just the same
quantity of metal as was deposited at the cathode. This action
REDUCTION OF ALUMINIUM COMPOUNDS. 3OS
exactly counterbalances the electromotive force required for
decomposition, and leaves only the conduction resistance of the
bath to be overcome. If this resistance is kept down so that
the tension required to operate the bath is less than or not
much greater than 1.5 volts, and the bath is well supplied with
salt, there will be no water decomposed and a good plating
may be obtained. This has been already practised on a large
scale with aluminium.
With anodes, however, which do not dissolve, the decom-
position of the salt necessarily involves that of the water, if over
1.5 volts are required to decompose it. The result of this is
that hydrogen gas is set free liberally at the cathode along with
the metal, and prevents the latter from depositing as a smooth,
dense metal, causing, in fact, the production of "sponge."
This finely-divided spongy metal is in the very best condition
to decompose water, and the result is its oxidation. However,
the metal can only decompose water at a certain rate ; the oxi-
dation does not take place instantaneously. If then we de-
posit the metal faster than it can waste away by oxidation, by
using a current of large quantity, we may succeed in gaining
metal and thus secure a deposit. This way of overcoming the
difficulty is assisted by using a very strong solution, which al-
lows a current of large quantity to pass with less resistance,
and also leaves less water uncombined to act on the metal.
By using these devices, Bunsen was enabled to obtain even
metallic calcium from a solution of its chloride.
By the density of the current we mean the number of am-
peres passing through each unit of surface of cathode or de-
positing surface. If the density is very great, it is necessary
that a brisk circulation be kept up in the solution to bring fresh
quantities of salt into the sphere of action and to remove the
impoverished solution ; otherwise, if a deficiency of salt occurs,
the solvent is attacked. Rapid circulation therefore favors
regular working.
In any electrolytic bath, the tension and density of the cur-
rent determine which of the several ingredients present will be
2,06 ALUMINIUM.
decomposed. Let us assume two compounds present, A and B,
of which ^ is a weaker compound than By either one of them
may be water, or they may both be anhydrous salts. In such
a liquid bath, a current just strong enough to decompose A
will not afifect B. When the current is just strong enough to
decompose B, the product will be the elements of A with a
trace of those of B/ but since the base in B is supposed to be a
stronger one than that in A, there will be a secondary action,
and the base of B will displace the base of A in the still unde-
composed compound, and B will be re-formed. This will be
the direct effect of increasing the tension of the current. How-
ever, if the density of the current is increased at the same time,
another principle comes into play. The base of B may be de-
posited so quickly that it has not time to react on A, and in
that case the deposit will contain the base of B. Also, if there
is a much larger proportion of B than of A present, a larger
proportion of its base will be deposited than before and escape
re-solution. Also, other things being equal, if the compound
B is more fluid or rather diffuses quicker in the bath than A,
more of it will get to the electrodes and a larger proportion be
decomposed.
We therefore see that when two or more compounds are
present, the relative amounts of each to be decomposed depend
1. Primarily, on the electro-motive force of the current,
which may be so regulated as to decompose them one after the "
other in the order of their electromotive force of decomposition.
2. On the density of the current at the electrodes. That is,
provided the tension of the current is sufficient to decompose
the stronger compound, the greater the density of the current
the greater the proportion of the stronger compound which
will be decomposed, other conditions being equal.
3. On the relative amounts of each present. Other condi-
tions being equal, the relative amount of a compound decom-
posed will increase as its proportion in the bath is increased.
4. On the relative rates of diffusion, or the rapidity with
which elements of the different compounds move towards the
electrodes.
REDUCTION OF ALUMINIUM COMPOUNDS. 307
The consideration of the electrolytic processes falls naturally
under two heads : —
I. Deposition from aqueous solution.
II. Non-aqueous electric processes.
I.
Deposition of Aluminium from Aqueovs Solution.
The status of this question is one of the curiosities of electro-
metallurgic science. Evidently attracted by the great reward
to be earned by success, many experimenters have labored in
this field, have recommended all sorts of processes, and pat-
ented all kinds of methods. We have inventors afiSrming in
the strongest manner the successful working of their methods,
while other experimenters have followed these recipes, and
tried almost every conceivable arrangement, yet report negative
results. To show that it is quite possible that many strong af-
firmations may be made in good faith, I have only to mention
the fact that in March, 1863, Mr. George Gore described in the
Philosophical Magazine some experiments by which he de-
posited coatings of aluminium from aqueous solutions, and
afterwards, in his text book of Electro-metallurgy, asserts that
he knows of no successful method of doing this thing. We
infer that Mr. Gore found that he was in error the first time.
So, if we take the position that aluminium cannot by any
methods so far advanced be deposited from aqueous solution
without using a soluble aluminium anode, we will have to ad-
mit that the proposers of many of the following processes are
probably misled by their enthusiasm in affirming so strongly
that they can do this thing. Yet the problem is not impossible
of solution.
Messrs. Thomas and Tilly* coat metals with aluminium and
its alloys by using a galvanic current and a solution of freshly
precipitated alumina dissolved in boihng water containing po-
tassium cyanide, or a solution of freshly calcined alum in
* English Patent, 1855, No. 2756.
308 ALUMINIUM.
aqueous potassium cyanide; also from several other liquids.
Their patent covers the deposition of the alloys of aluminium
with silver, tin, copper, iron, silver and copper, silver, and tin,
etc. etc., the positive electrode being of this metal or alloy.
M. Corbelli, of Florence,* deposits aluminium by electroylz-
ing a mixture of rock alum or sulphate of alumina (2 parts)
with calcium chloride or sodium chloride (i part) in aqueous
solution (7 parts), the anode being mercury placed at the
bottom of the solution and connected to the battery by an iron
wire coated with insulating material and dipping its uncovered
end into the mercury. The zinc cathode is immersed in the
solution. Aluminium is deposited on the zinc, as a blackish
powder or as a thin, compact sheet, and the chlorine which is
liberated at the anode unites with the mercury, forming calomel.
J. B. Thompsonf reports that he has for over two years been
depositing aluminium on iron, steel, and other metals, and
driving it into their surfaces at a heat of 500° F., and also de-
positing aluminium bronze of various tints, but declines to state
his process.
George Gore, Jthe noted electrician, recommended the fol-
lowing procedure for depositing aluminium on copper, brass, or
German silver: —
" Take equal measures of sulphuric acid and water, or one
part sulphuric acid, one part hydrochloric acid and two parts
of water, put into it half an ounce of pipe clay to the pint of
dilute acid, and boil for an hour. Take the clear, hot liquid
and immerse in it an earthen porous cell containing sulphuric
acid diluted with ten times its bulk of water, together with a
rod or plate of amalgamated zinc. Connect the zinc with the
positive wire of a Smee battery of three or four elements con-
nected for intensity. The article to be coated, well cleaned, is
connected with the negative pole and immersed in the hot clay
solution. In a few minutes a fine, white deposit of aluminium
* English Patent, 1858, No. 507.
fChem. News, xxiv. 194 (1871).
t Philosophical Magazine, March, 1863.
REDUCTION OF ALUMINIUM COMPOUNDS. 309
will appear all over its surface. It may then be taken out,
washed quickly in clean water, wiped dry, and polished. If a
thicker coating is required, it must be taken out as soon as the
deposit becomes dull, washed, dried, polished, and re-immersed,
and this must be repeated at intervals as often as it becomes
dull, until the required thickness is obtained. It is necessary
to have the acid well saturated by boiling, or no deposit will
be obtained."
Mierzinski asserts that Dr. Gore was mistaken when he sup-
posed this deposit to be aluminium, and in Gore's Text Book
of Electro-metallurgy no mention is made of these experi-
ments, the author thereby acknowledging the error. As to
what the deposit could have been, we are left to conjecture,
since no explanation has been advanced by Dr. Gore ; it may
possibly have been silicon, mercury, or zinc, as all three of
these were present besides aluminium.
J. A. Jeanfon* has patented a process for depositing alumin-
ium from an aqueous solution of a double salt of aluminium
and potassium of specific gravity 1.161 ; or from any solution
of an aluminium salt, such as sulphate, nitrate, cyanide, etc.,
concentrated to 20° B. at 50° F. He uses a battery of four
pairs of Smee's or three Bunsen's cells, with elements arranged
for intensity, and electrolyzes the solutions at 140° F. The
first solution will decompose without an aluminium anode, but
the others require such an anode on the negative pole. The
solution must be acidulated slightly with acid corresponding to
the salt used, the temperature being kept at 140° F. constantly.
More recently!, Jeangon has obtained a patent for the fol-
lowing process : " Subjecting a supersaturated acid solution of
a salt of aluminium to the action of a current passed from an
anode of aluminium in a state of division or porosity, pre-
senting a relatively large exposure of surface within a given
field of electric force, and a suitable metallic cathode." Further
* Annual Record of Science and Industry, 1875.
tU. S. Patent, 436,895; Sept. 23, i8go. (Specimens.)
3IO ALUMINIUM.
details state that the anode is to be prepared by melting alu-
minium iri a crucible and stirring in about 30 per cent, of car-
bon or a similar substance, and then moulding into shape. The
electrolyte is to be maintained at a high temperature, preferably
180° to 200° F., under which conditions a dense deposit is
obtained.
The writer has already stated that aluminium is being suc-
cessfully electro-plated from solution using aluminium anodes;
and, if the above process is the one which has been used in
Philadelphia by the Harvey Filley Plating Co., then I can cer-
tify to it having been successfully operated. The company
mentioned refuse to say anything about the process they use,
but I have been informed by outside parties that the above is
the one. It is certain, however, that very good specimens of
aluminium-plated ware have been made and sold by this firm,
several having been examined and tested by the writer person-
ally. A thin deposit on sheet-iron, which has been in my pos-
session over two years, shows no sign of rust or deterioration,
and suggests the practicability of thus making a substitute for
tin-plate of greater durability and which will not rust.
M. A. Bertrand * states that he deposited aluminium on a
plate of copper from a solution of double chloride of aluminium
and ammonia, by using a strong current, and the deposit was
capable of receiving a brilliant polish.
Jas. S. Haurd,t of Springfield, Mass., patented the elec-
trolysis of an aqueous solution formed by dissolving cryolite in
a solution of magnesium and manganous chlorides.
John Braun { decomposes a solution of alum, of specific
gravity 1.03 to 1.07, at the usual temperature, using an insolu-
ble anode. In the course of the operation, the sulphuric acid
set free is neutralized by the continual addition of alkali ; and,
afterwards, to avoid the precipitation of alumina, a non-volatile
organic acid, such as tartaric, is added to the solution. The
* Chem. News, xxiv. 227.
t U. S. Patent, 228,900, June 15, 1880.
X German Patent, No. 28,760 (1883'!.
REDUCTION OF ALUMINIUM COMPOUNDS. 3 II
intensity of the current is to be so regulated that for a bath of
lO to 20 Htres two Bunsen elements (about 20 centimetres
high) are used.
Dr. Fred. Fischer* stated that Braun's proposition was con-
trary to his experience. By passing a current of 8 to 9 volts
and 50 amperes, using from o.i to 10 amperes per sq. centi-
metre of cathode, with various neutral and basic aluminium
sulphate solutions, with and without organic acids, he obtained
no aluminium. He obtained a black deposit of copper sul-
phide on the copper anode, which had apparently been mis-
taken by Braun for aluminium.
Moses G. Farmer | has patented an apparatus for obtaining
aluminium electrically, consisting of a series of conducting cells
in the form of ladles, each ladle having a handle of conducting
material extending upwards above the bowl of the next suc-
ceeding ladle ; each ladle can be heated separately from the
rest ; the anodes are hung in the ladles, being suspended from
the handles of the preceding ladles, the ladles themselves being
the cathodes.
M. L. Senet X electrolyzes a saturated solution of aluminium
sulphate, separated by a porous septum from a solution of
sodium chloride. A current is used of 6 to 7 volts and 4
amperes. The double chloride, AlCl'.NaCl, is formed, then
decomposed, and the aluminium liberated deposited on the
negative electrode. It has later been remarked of this process
that it has not had the wished-for success on a large scale.
Col. Frismuth, of Philadelphia, purported to plate an alloy of
nickel and aluminium. He used an ammoniacal solution, prob-
ably of their sulphates. The plating certainly resembled
nickel, but that it contained aluminium the writer is not pre-
pared to assert.
Baron Overbeck and H. Neiwerth, of Hannover, § have
* Zeitschrift des Vereins Deutsche Ingenieurs, 1884, p. 557.
t U. S. Patent, No. 315,266, April, 1885.
t Cosmos les Mondes, Aug. 10, 1885.
§ English Pat., Dec. 15, 1883, No. 5756:
3 1 2 ALUMINIUM.
patented the following process : An aqueous or other solu-
tion of an organic salt of aluminium is used, or a mixture of
solutions which by double decomposition will yield such salt.
Or a mixture of a metallic chloride and aluminium sulphate
may be used, this yielding nascent aluminium chloride, which
the current splits up immediately into aluminium and chlorine.
Herman Reinbold* gives the following recipe, stating that it
furnishes excellent results : 50 parts of potash alum are dis-
solved in 300 parts of water, and to this are added 10 parts of
aluminium chloride. The whole is then heated to 200° F.,
cooled, and then 39 parts of potassium cyanide added. A
weak current should be used. It is stated that the plating,
when polished, will be found equal to the best silver plating.
" Iron," noticing this process, remarks, " there are a number of
formulae for electro-plating with aluminium, but few appear to
have attained to practical utility in the arts, for the reason that
there is no special demand for such processes. All the quali-
ties that are possessed by an electro-deposit of aluminium are
possessed to an equal or superior degree by other metals, silver,
nickel, platinum, etc. Furthermore, it obstinately refuses to
take and to retain a high lustre." This criticism is a little
overdrawn, since the one quality in which aluminium is super-
ior to silver — not blackening by contact with sulphurous vapor
— is not mentioned.
Under the name of Count R. de Montegelas, of Philadelphia,
several patents have been taken out in England for the elec-
trolysis of aqueous solutions, which may be summarized as
follows : —
f Alumina is treated with hydrochloric acid, and aluminium
chloride obtained in solution. The liquid is then placed in a
vessel into which dip a suitable anode and a cathode of brass or
copper. On passing an electric current through the bath the
iron present in the liquid is first deposited, and as soon as this
deposition ceases (as is apparent by the change of color of the
* Jeweler's Journal, September, 1887.
t English Patent, Aug. 18, 1886, No. 10607.
REDUCTION OF ALUMINIUM COMPOUNDS. 313
deposit) the liquid is decanted into another similar bath, and to
it is added about fifty per cent, by weight of the oxide of either
lead, tin or zinc. On sending a current through this bath,
aluminium together with the metal of the added oxide is said to
be deposited on the cathode.
* A rectangular vessel is divided into two unequal compart-
ments by a vertical porous partition, into the smaller of which
is placed a saturated solution of common salt, in which is im-
mersed a brass or copper electrode ; into the larger is put a so-
lution of aluminium chloride, immersed in which is an alumin-
ium electrode. On passing the current the latter solution,
which is normally yellow, is gradually decolorized and con-
verted into a solution of aluminium-sodium chloride. When
colorless, this solution is taken out and the aluminium deposited
in a similarly arranged vessel. The double chloride solution is
placed in the larger compartment, with an electrode of brass,
copper, or a thin plate of aluminium, while the smaller com-
partment contains a carbon electrode dipping into a solution of
salt and surrounded by fragments of a mixture of salt and
double chloride, fused together in equal parts.
The author has been given several ounces of a very fine me-
tallic powder said to have been made by these processes, and
which is certainly aluminium. As I am not satisfied, however,
that the specimen is really authentic, I feel justified in suspend-
ing a final expression of opinion on the process.
A Walker, of Tarnowitz, has patented the following methods
of procedure : j
a. Pure commercial hydrate is dissolved in nitric acid free
from chlorine, in slight excess, and tartaric acid added. The
Hquid is let clear for some time, any potassium bi-tartrate,
which may be formed from small quantities of potassium ad-
hering to the hydrate, filtered out, and the clear solution
electrolyzed. There is added to the solution during electrolysis
* English Patent, Feb. 3, 1887, No. 1751.
t German Pat. (D. R. P.) 40,626 (1887).
3 1 4 ALUMINIUM.
organic acid — as formic, acetic, citric, oxalic — or, better, ab-
solute alcohol.
b. A solution of aluminium nitrate, as far as possible free
from alkalies and sulphuric acid, is decomposed by a strong
dynamic current in baths arranged in series, using platinized
plates as anode and cathode. With a weak current of 0.02 to
0.05 amperes to a square centimetre, the aluminium separates
out on the cathode as a deep black deposit, sticking close to
the copper. The cathode is lifted from the solution, freed from
small quantities of alumina coating it by gentle rinsing, and
then the deposit washed off by a strong jet of water. The
powder obtained is washed further with clear, cold water, par-
ticularly free from sodium chloride, and dried by gentle heat-
ing in the air.
H. C. Bull* proposes to manufacture aluminium alloys by
using the metal to be alloyed with aluminium as a cathode in a
bath of aluminium sulphate, the anode being either of alumin-
ium or of an insoluble substance. When enough aluminium is
deposited, the cathode is taken out and melted down.
C. A. Burghardt and W. J. Twining, of Manchester, England,
have patented the following methods :
fTo a solution of sodium or potassium aluminate containing
about 7.2 oz. of aluminium per gallon are added 4 pounds of
95 per cent, potassium cyanide dissolved in a quart of water,
and then gradually 2j^ pounds of potassium bi-carbonate.
The whole is boiled 12 hours and made up to a gallon. The
bath is used at 175° F. with aluminium or platinum anode and
carbon or copper cathode. The addition of a little free hydro-
cyanic acid insures a bright deposit when articles are being
plated.
% Two and one-half kilos of aluminium sulphate in solution is
precipitated by ammonia, and then re-dissolved by adding \yi
kilos of caustic soda dissolved in a litre of water; the alumina
♦English Pat., 10,199 A. (1887).
t English Pat., July 2, 1887, No. 9389.
I German Pat. (D. R. P.), 45,020 (1887).
REDUCTION OF ALUMINIUM COMPOUNDS. 3x5
is thus slightly in excess. The hydrocyanic acid is added until
a slight precipitate appears. This solution, warmed to 80°, is
used as a bath from which aluminium is to be deposited.
*The bath is prepared by dissolving alumina in a solution of
chloride of copper, and treating further with caustic soda or
potash for the purpose of causing the aluminium and copper to
combine together. The precipitate, dissolved in hydrocyanic
acid and diluted, forms a bath of double cyanide, which when
electrolyzed deposits an alloy of aluminium and copper.
Besides the processes so far described, patents have been
taken out in England by Gerhard and Smith,f Taylor,| and
Coulson,§ the details of which have not been accessible to the
author.
Over against these statements of enthusiastic inventors, let
me place a few extracts from authorities who have given much
time and attention to the subject of electro-depositing alumin-
ium from solution without the use of an aluminium anode.
Sprague|| states his inability to deposit aluminium electric-
ally from solution.
Dr. Clemens Winckler IT states that he has spent much time
in trying all methods so far proposed, and comes to the conclu-
sion that aluminium cannot be deposited by electricity in the
wet way.
Dr. Geo. Gore** although having once proposed a method
which he said attained this end, yet in his later work on Elec-
tro-metallurgy does not mention his former proposition, and
quotes, apparently as coinciding with his own opinion, the
words of Sprague and Winckler given above.
* English Pat., Oct. 28, 1887, No. 2602.
tNo. 16,653 (1884).
J No. 1991 (1855).
§ No. 207s (1857).
II Sprague's Electricity, p. 309.
t Journal of the Chem. Soc, X. 1 134.
** Text-book of Electto- metallurgy.
3l6 ALUMINIUM.
Dr. S. Mierzinski* states, in 1883, that "the deposition of
aluminium from an aqueous solution of its salt has not yet been
accomplished."
Dr. W. Hampef claims to have shown that the electrolysis
of aqueous aluminous solutions, although frequently patented,
is not to be expected. From which we would infer that he
could not testify to it ever having been done.
Alexander Watt| holds that the electrolytic production of
aluminium ,from solution is very improbable. He tried acid
solutions, alkaline solutions, cyanide combinations, etc., under
most varied conditions, without any result.
Finally, I will quote from a letter of my good friend Dr.
Justin D. Lisle, of Springfield, O., who with ample means at
his disposal, an enthusiasm bred of love tor scientific truth, and
talent to guide him in his work, has reached the following re-
sults : " I have tried in almost every conceivable way to de-
posit it (aluminium) from aqueous solution by electricity,
using from i pint cells to 60 gallon cells successively ; the cells
were connected for quantity and for intensity; acid and neutral
solutions were used; carbon, platinum, and copper electrodes,
porous cups and diaphragms, were all thoroughly tried, without
the slightest deposit of metal. In some cases alumina was de-
posited, which has led me to think that aluminium was pri-
marily deposited, and owing to the fine state in which it existed
was promptly oxidized."
The following details of the operation of the electric plant of
the Tacony Metal Company, near Philadelphia, under the
supervision of Mr. J. D. Darling, are all that the writer has
been able to gather respecting their process. This company
had the contract to electroplate the exterior ironwork of the
tower of the Philadelphia Public Buildings, there being alto-
gether about 50,000 square feet to be plated, on which was to
be deposited 20,000 pounds of aluminium, or a little over six
* Die Fabrikation des Aluminiums.
tChem. Zeit. (Cothen), XI. 935.
I London Electrical Review, July, 1887.
REDUCTION OF ALUMINIUM COMPOUNDS. 317
ounces to the foot. This would give a smooth coating j\ inch
thick. The cast-iron work is first given a coating of copper,
and the aluminium deposited on it, but it is stated that good
platings have been obtained directly on the cast-iron.
The largest pieces plated were columns 26 feet long and 3
feet in diameter. The whole operation of treating such a col-
umn lasted 1 1 days, while the plant could turn out one every
4 days. The operations were as follows :
(i) Boiling 24 hours in a strong solution of caustic soda,
after which well washed.
(2) Pickled in dilute sulphuric acid 24 hours, brushed vig-
orously and washed.
(3) Copper-plated by immersion 40 hours in a copper
cyanide(?) solution. The column was then brushed with par-
affine wax inside, any flaws soldered up, and —
(4) Copper-plated again in an ordinary copper-plating so-
lution for 72 hours, until 16 ounces of copper to the square
foot had been deposited.
(5 ) Put into the aluminium-plating tank, and 3 ounces of
aluminium per square foot deposited on it. Time, 72 hours.
Column then well washed in the sixth tank.
The dynamo used for operation 3 gives a current of 1000
amperes at 6 volts tension ; for operation 4, 4000 amperes
at 2.5 volts tension; for operation 5, 2000 amperes at 8 volts
tension. In the latter case, the current density at the depos-
iting surface was 8 amperes per square foot (86 amperes per
square metre). In this depositing tank, aluminium anodes 4
feet long, 12 inches wide and }( inch thick were used. Sixty
of these plates, weighing 35 pounds each, were hung around
the inside of the tank.
■ The company will give no information regarding the compo-
sition of the electrolyte. Concerning the conducting of thS
operation, Mr. Darling has stated that " Aluminium is more
difficult to deposit than any of the common metals, because of
its tendency to re-dissolve after being deposited. I find that
by using a solution of aluminium salt that has but a slight dis-
3l8 ALUMINIUM.
solving effect on aluminium, with a density of current of 8
amperes per square foot, and with sufficiently high voltage,
aluminium can be deposited at the rate of i gramme per hour
per square foot in a reguline state. With much higher cur-
rents it can be deposited quicker, but will be in a pulverulent
state, which does not adhere."
II.
Non-aqueous Electric Processes.
The above heading was originally written, "The electrolytic
decomposition of fused aluminium compounds," but I have
changed it to this form because it is doubtful, in several cases,
whether electrolytic decomposition really plays much of a role
in the isolation of the aluminium. In some processes a pow-
erful current is used and largely converted into heat, producing
temperatures never before used in industrial operations. In
such cases, chemical reactions, rendered possible by the very
high temperature, come into play and may even be the prin-
cipal means of reducing the aluminium compound. It has been
suggested that such processes should be classed apart as
"electro-thermal methods;" but such a division does not ap-
pear satisfactory to me, because in most cases we cannot say
positively that electrolysis does not play some part, and in
others it is simply impossible to decide which of the two agents
of reduction, electrolysis or chemical affinity, is the most active.
It has been suggested also that those processes in which high
voltage is used cannot be electrolytic, but must be electro-ther-
mal ; but such a division is not logical. If a bath is taking a
high voltage to work it, it may be solely from poor conductivity
in the electrolyte, and not because an arc is formed in the bath,
and true electrolysis may be going on to the full extent of the
power of the current. If we knew definitely, for each process,
which action played the principal part in the reduction, we
might classify the processes, but such a classification would not
be of much use. If it was absolutely necessary to make some
REDUCTION OF ALUMINIUM COMPOUNDS. 319
such division, I should consider as electro-thermal those pro-
cesses in which the parts of the apparatus used are not ar-
ranged as they should be to secure the maximum electrolytic
decomposition. We could thus, in such cases, say at once,
from a consideration of the apparatus and its manner of work-
ing, that electrolysis was evidently not contemplated in its con-
struction and could only play a minor part in its operation.
In conclusion, I regard it impossible to make an exact clas-
sification of these processes such as would be of any value to
the metallurgist or aid the general reader to a better under-
standing of them, and I therefore take them up in chronolog-
ical order.
Davy's Experiment (1810).
Sir Humphry Davy, in his Brompton Lecture before the
Royal Philosophical Society,* described the following attempt
to decompose alumina and obtain the metal of this earth. He
connected an iron wire with the negative pole of a battery con-
sisting of 1000 double plates. The wire was heated to white-
ness and then fused in contact with some moistened alumina,
the operation being performed in an atmosphere of hydrogen.
The iron became brittle, whiter, and on being dissolved in acid
gave a solution from which was precipitated alumina, identical
with that used.
It is evident that the alumina had been reduced by the
chemical action of the hydrogen gas, a reaction which we now
know takes place below the fusing point of alumina, 2200°, and
probably begins as low as 1700°.
Duvivier's Experiment (1854).
M. Duvivier f states that by passing an electric current from
eighty Bunsen cells through a small piece of laminated disthene
between two carbon points, the disthene melted entirely in two
or three minutes ; the elements which composed it were partly
* Philosophical Transactions, 1810.
fThe Chemist, Aug., 1854.
320 ALUMINIUM.
disunited by the power of the electric current, and some alu-
minium freed from its oxygen. Several globules of the metal
separated, one of which was as white and as hard as silver.
Since disthene is aluminium silicate, formula Al^Os.SiOj, it
is most likely that the metal obtained was highly siliceous
aluminium, since complete reduction of this compound would
give 54 parts of aluminium to 28 parts of silicon. The highly-
heated carbon particles of the electric arc were most probably
the reducing agent.
Bunsen's and Deville's Methods (1854).
A method of decomposing aluminium-sodium chloride by the
battery was discovered simultaneously by Deville in France and
Bunsen in Germany, in 1854, and is nothing else but an appli-
cation of the process already announced by Bunsen of decom-
posing magnesium chloride by the battery. Deville gives the
more minute account, and we therefore quote his description of
the process.
f " It appears to me impossible to obtain aluminium by the
battery in aqueous solutions. I should believe this to be an
absolute impossibility if the brilliant experiments of M. Bunsen
in the preparation of barium, chromium and manganese did not
shake my convictions. Still I must say that all the processes
of this description which have recently been published for the
preparation of aluminium have failed to give me any results.
Every one knows the elegant process by means of which M.
Bunsen has lately produced magnesium, decomposing fused mag-
nesium chloride by an electric current. The illustrious profes-
sor at Heidelberg has opened up a method which may lead to
very interesting results. However, the battery cannot be used
for decomposing aluminium chloride directly, which does not
melt, but volatilizes at a low temperature ; it is, therefore, neces-
sary to use some other material which is fusible and in which
*Tbe Chemist, Aug. 1854.
t Ann. de Chem. et de Phys. [3], 46, 452; Deville's " de rAluminium."
REDUCTION OF ALUMINIUM COMPOUNDS. 321
aluminium alone will be displaced by the current. I have found
this salt in the double chloride of aluminium and sodium, which
melts towards 185° C, is fixed at a somewhat high temperature,
although volatile below the fusing point of aluminium, and thus
unites all the desirable conditions.
" I put some of this double chloride into a porcelain crucible
separated imperfectly into two compartments by a thin leaf of
porcelain, and decomposed it by means of a battery of five ele-
ments and carbon electrodes. The crucible was heated more
and more as the operation progressed, for the contents became
less and less fusible, but the heat was not carried past the melt-
ing point of aluminium. Arrived at this point, after having
lifted out the diaphragm and electrodes, I heated the crucible
to bright redness, and found at the bottom a button of alumin-
ium, which was flattened out and shown to the Academy in the
S6ance of March 20, 1854. The button was accompanied by a
considerable quantity of carbon, which prevented the union of
a considerable mass of shot-metal. This carbon came from the
disintegration of the very dense gas-retort carbon electrodes; in
fact, the positive electrode was entirely eaten away in spite of
its considerable thickness. It was evident, then, that this appa-
ratus, although similar to that adopted by Bunsen for manufac-
turing magnesium, would not suit here, and the following is the
process which after many experiments I hold as best.
" To prepare the bath for decomposition, I heat a mixture of
2 parts aluminium chloride and i part sodium chloride, dry and
pulverized, to about 200° in a porcelain capsule. They com-
bine with disengagement of heat, and the resulting bath is very
fluid. The apparatus which I use for the decomposition com-
prises a glazed porcelain crucible, which as a precaution is
placed inside a larger one of clay. The whole is covered by a
porcelain cover pierced by a slit to give passage to a large thick
leaf of platinum, which serves as the negative electrode ; the lid
has also a hole through which is introduced, fitting closely, a
well-dried porous cylinder, the bottom of which is kept at some
distance from the inside of the porcelain crucible. This porous
322
ALUMINIUM.
vessel encloses a pencil of retort carbon, which serves as the
positive electrode. Melted double chloride is poured into the
porous jar and into the crucible so as to stand at the same
height in both vessels ; the whole is heated just enough to keep
the bath in fusion, and there is passed through it the current
from several Bunsen cells, two cells being strictly sufficient.
The annexed diagram shows the crucibles in section.
Fig. 28.
"The aluminium deposits with some sodium chloride on the
platinum leaf; the chlorine, with a little aluminium chloride, is
disengaged in the porous jar and forms white fumes, which are
prevented from rising by throwing into the jar from time to
time some dry, pulverized sodium chloride. To collect the
aluminium, the platinum leaf is removed when sufficiently
charged with the saline and metallic deposit; after letting it
cool, the deposit is rubbed off and the leaf placed in its former
position. The material thus detached, melted in a porcelain
crucible, and after cooling washed with water, yields a gray,
metallic powder, which by melting several times under a layer
of the double chloride is reunited into a button."
Bunsen* adopted a similar arrangement. The porcelain cru-
* Pogg. Annalen, 97, 648.
REDUCTION OF ALUMINIUM COMPOUNDS. 323
cible containing the bath of aluminium-sodium chloride kept in
fusion was divided into two compartments in its upper part by a
partition, in order to separate the chlorine liberated from the alu-
minium reduced. He made the two electrodes of retort carbon.
To reunite the pulverulent aluminium, Bunsen melted it in a bath
of the double chloride, continually throwing in enough sodium
chloride to keep the temperature of the bath about the fusing
point of silver.
As we have seen, Deville, without being acquainted with Bun-
sen's investigations, employed the same arrangement, but he
abandoned it because the retort carbon slowly disintegrated in
the bath, and a considerable quantity of double chloride was lost
by the higher heat necessary to reunite the globules of alumin-
ium after the electrolysis. Deville also observed that by working
at a higher temperature, as Bunsen had done, he obtained purer
metal, but in less quantity. The effect of the high heat is that
silicon chloride is formed and volatilizes, and the iron which
would have been reduced with the aluminium is transformed
into ferrous chloride by the aluminium chloride, and thus the
aluminium is purified of silicon and iron.
Plating aluminium on copper. — The same bath of double chlor-
ide of aluminium and sodium may be used for plating alumin-
ium in particular on copper, on which Capt. Caron experimented
with Deville. Deville says : " To succeed well, it is necessary to
use a bath of double chloride which has been entirely purified
from foreign metallic matter by the action of the battery itself.
When aluminium is being deposited at the negative pole, the first
portions of metal obtained are always brittle, the impurities in
the bath being removed in the first metal thrown down; so,
when the metal deposited appears pure, the piece of copper to
be plated is attached to this pole and a bar of pure aluminium
to the positive pole. However, a compact mixture of carbon
and alumina can be used instead of the aluminium anode, which
acts similarly to it and keeps the composition of the bath con-
stant. The temperature ought to be kept a little lower than the
fusing point of aluminium. The deposit takes place readily
324 ALUMINIUM.
and is very adherent, but it is difficult to prevent it being im-
pregnated with double chloride, which attacks it the moment
the piece is washed. The washing ought to be done in a large
quantity of water Cryolite might equally as well be used for
this operation, but its fiisibility should be increased by mixing
with it a little double chloride of aluminium and sodium and
some potassium chloride."
During a recent law-suit for infringement of the Hall process,
it was held by the defendants that Deville electrolyzed a fluoride
bath, (cryolite) in which alumina was present and therefore
would be dissolved. It appears quite evident, however, that
Deville did not use cryolite, because it would have destroyed
the porcelain crucibles and necessitated the use of special ap-
paratus which Deville does not even hint at. It is, moreover,
true that when alumina is mixed with carbon the latter prevents
the cryoHte from wetting or coming into actual contact with it.
In an experiment by the writer, a large cylinder of carbon into
which had been incorporated over 50 per cent, of alumina
was kept in molten cryolite for several hours, and on being
taken out showed not the slightest sign of corrosion. Judges
Taft and Ricks of Ohio very properly ruled that Deville's ex-
periments did not in any way disclose or operate on the princi-
ple utilized by Mr. Hall.
Le Chatellier's Method (1861).
The subject of this patent* was the decomposition of the
fused double chloride of aluminium and sodium, with the par-
ticular object of coating or plating other metals, the articles
being attached to the negative pole. About the only novelty
claimed in this patent was the use of a mixture of alumina and
carbon for the anode, but we see from the previous paragraph
that this was suggested by Deville several years before ; the
only real improvement was the placing of this anode inside a
porous cup, in order to prevent the disintegrated carbon from
* English Patent, 1861, No. 1214.
REDUCTION OF ALUMINIUM COMPOUNDS. 325
falling into the bath. This was really only the Deville process,
patented in England.
Monckton's Patent (1862).
Monckton* proposes to pass an electric current through a
reduction chamber, and in this way to raise the temperature
to such a point that alumina will be reduced by the carbon
present. We clearly see in this the germ of several more-
recently patented processes.
Gaudin's Process (1869).
Gaudin f reduces aluminium by a process to which he ap-
plies the somewhat doubtful title of economic. He melts to-
gether equal parts of cryolite and sodium chloride, and traverses
the fused mass by a galvanic current. Fluorine is evolved at
the positive pole, while aluminium accumulates at the negative.
The great difficulties in such a process are the obtaining of
suitable vessels to withstand the corrosion of the bath, the great
inconvenience of the escaping fluoride gas, and the increase of
resistance due to the change of composition of the bath. It
would need several additional patents to render this process
operative, without mentioning economy.
Kagensbusch' s Process (1872).
Kagensbusch,! of Leeds, proposes to melt clay with fluxes,
then adding zinc or a like metal to pass an electric current
through the fused mass, isolating an alloy of aluminium and
the metal, from which the foreign metal may be removed by
distillation, sublimation, or cupellation.
If the patentee had used pure alumina instead of clay, he
might have produced some aluminium by his process, but the
silicon in the clay would get into the zinc in larger proportion
* English Patent, 1862, No. 264.
t Moniteur Scientifique, xi., 62.
X English Patent, 1872, No. 481 1.
326 ALUMINIUM.
than the aluminium, rendering the succeeding operations for
obtaining pure aluminium impossible.
Berthaut's Proposition (1879).
Up to this time all the proposed electric processes were
confined to the use of a galvanic current, the cost of obtaining
which was a summary bar to all ideas of economical produc-
tion. About this period dynamo-electric machines were being
introduced into metallurgical practice, and Berthaut is the first
we can find who proposes their use in producing aluminium.
The process which he patented * is otherwise almost identical
with Le Chatellier's,
Grdtzel's Process (1883).
This process f has little claim to originality, except in the
details of the apparatus. A dynamo-electric current is used,
the electrolyte is fused cryolite or double chloride of aluminium
and sodium, and the anodes are of pressed carbon and alumina
— none of which points are new. However, the use of melting
pots of porcelain, alumina, or aluminium, and making them the
negative electrode, are points in which innovations are made.
In a furnace are put two to five pots, according to the power
of the dynamo used, each pot having a separate grate. The
pots are preferably of metal, cast-steel is used, and form the
negative electrodes. The positive electrode, K (Fig. 29), can
be made of a mixture of anhydrous alumina and carbon pressed
into shape and ignited. A mixture of alumina and gas-tar
answers very well ; or it can even be made of gas-tar and gas-
retort carbon. During the operation little pieces of carbon fall
from it and would contaminate the bath, but are kept from
doing so by the mantle G. This isolated vessel, G, is perforated
around the lower part at g, so that the molten electrolyte may
circulate through. The tube O' conducts reducing gas into the
* English Patent, 1879, No. 4087.
t German Patent (D. R. P.), No. 26962 (1883).
REDUCTION OF ALUMINIUM COMPOUNDS.
327
crucible, which leaves by the tube 0\ This reducing atmos-
phere is important, in order to protect from burning any metal
rising to the surface of the bath. The chlorine set free at the
electrode, K, partly combines with the alumina in it, regenera-
ting the bath, but some escapes, and, collecting in the upper
part of the surrounding mantle, G, is led away by a tube con-
FlG. 29.
necting with it. Instead of making the electrode K of carbon
and alumina, it may simply be of carbon, and then plates of
pressed alumina and carbon are placed in the bath close to the
electrode, K, but not connected with it. Also, in place of
making the crucible of metal and connecting it with the nega-
tive pole, it may be made of a non-conducting material, clay or
the like, and a metallic electrode — as, for instance, of alu-
minium— plunged into the bath.
In a later patent,* Gratzel states that the bath is decomposed
* English Patent; 14325, Nov. 23, 1885. U. S. Patent, 362441, May 3, 1887.
328 ALUMINIUM.
by a current of comparatively low tension if magnesium chloride
be present ; the chlorides of barium, strontium or calcium act
similarly.
Prof. F. Fischer* maintains as impracticable the use of plates
of pressed alumina and carbon, which can, further, only be
operative when they are made the positive electrode, and then
their electric resistance is too great. The incorporation into
them of copper filings, saturation with mercury, etc., give no
more practical results. There are also volatilized at the anodes
considerable quantities of aluminium chloride, varying in
amount with the strength of the current.
Large works were erected near Bremen by the Aluminium
und Magnesiumfabrik Pt. Gratzel, zu Hemelingen, in which
this process was installed. License was also granted to the
large chemical works of Schering, at Berlin, to operate it. R.
Biedermann, in commenting on the process in i886,f stated
that the results obtained so far were not fully satisfactory, but
the difficulties which had been met were of a kind which would
certainly be overcome. They were principally in the polariza-
tion of the cathode, by which a large part of the current was
neutralized. By using proper depolarizing substances this dif-
ficulty would be removed. The utilization of the chlorine
evolved would also very much decrease the expenses. A more
suitable slag, which collected the aluminium together better,
was also desirable. Finally, the metal produced was somewhat
impure, taking up iron from the iron pots and silicon from the
clay ones, to obviate which Biedermann recommended the use
of lime or magnesia vessels.
Prof. Fischer, as we have seen, maintained the uselessness of
Gratzel's patent claims, and his later expression of this opinion
in 1887 drew a reply from A. Saarburger, Jdirectorof the works
at Hemehngen, to the effect that since October, 1887, they had
* Wagner's Jahresbericht, 1884, p. 1319; 1887, p. 376.
fKerl und Stohman, 4th ed., p. 725.
{ Verein der Deutsche Ingenieure, Jan. 26, 1889.
REDUCTION OF ALUMINIUM COMPOUNDS. 329
abandoned the Gratzel process, and were making aluminium at
present by methods devised by Herr Saarburger; in conse-
quence of which fact the directors of the company decided in
January, 1888, to drop the addition Pt. Gratzel from the firm
name. The methods then in use at Hemelingen were kept secret,
but the author was informed by a friend in Hamburg that they
were using a modified Deville sodium process. Herr Saarbur-
ger informed me in October, 1888, that they were producing
pure aluminiuin at the rate of 12 tons a year, besides a large
quantity sold in alloys. An attractive pamphlet issued by this
firm set forth precautions to be used in making aluminium
alloys, together with a digest of their most important properties,
which we shall have occasion to quote from later in considering
those alloys.
The sharp decline in the price of aluminium in 1890 forced
this company out of the aluminium business.
Cowles Bros! Process.
Messrs. E. H. and A. H. Cowles patented in the United
States and Europe * an electric furnace and its application for
producing aluminium. Their patent claims " reducing an alu-
minium compound in company with a metal in presence of car-
bon in a furnace heated by electricity ; the alloy of aluminium
and the metal formed being further treated to separate out the
aluminium." The history of the development of this process
having already been sketched, we will proceed to describe the
details of its operation. The first public description was given
in two papers, one read before the American Association for the
Advancement of Science f by Prof. Chas. F. Mabery of the Case
School of Applied Science, Cleveland, the other before the
American Institute of Mining Engineers % by Dr. T. Sterry
Hunt, of Montreal.
* U. S. Patents 324658, 324659, Aug. 18, 1885; English Patent 9781, same date;
German Patent 33672.
t Ann Arbor Meeting, Aug. 28, 1885.
X Halifax Meeting, Sept. 16, 1885.
330 ALUMINIUM.
Prof. Mabery said in his paper : " Some time since, the Messrs.
Cowles conceived the idea of obtaining a continuous high tem-
perature on an extended scale by introducing into the path of
an electric current some material that would afford the requi-
site resistance, thereby producing a corresponding increase in
the temperature. After numerous experiments, coarsely pul-
verized carbon was selected as the best means for maintaining
an invariable resistance, and at the same time as the most
available substance for the reduction of oxides. When this
material, mixed with the oxide to be reduced, was made a part
of the electric circuit, inclosed in a fire-clay retort, and sub-
jected to the action of a current from a powerful dynamo, not
only was the oxide reduced, but the temperature increased to
such an extent that the whole interior of the retort fused com-
pletely. In other experiments lumps of lime, sand, and corun-
dum were fused, with a reduction of the corresponding metal ;
on cooling, the lime formed large, well-defined crystals, the
corundum beautiful red-green and blue octahedral crystals.
Following up these results, it was soon found that the intense
heat thus produced could be utilized for the reduction of oxides
in large quantities, and experiments were next tried on a large
scale with the current from a fifty horse-power dyamo. For
the protection of the walls of the furnace, which were of fire-
brick, a mixture of ore and coarsely pulverized gas-carbon was
made a central core, and was surrounded on the side and bot-
tom by fine charcoal, the current following the lesser resistance
of the core from carbon electrodes inserted in the ends of the
furnace in contact with the core. The furnace was charged by
first filling it with charcoal, making a trough in the centre, and
filling this with the ore mixture, the whole being covered with
a layer of coarse charcoal. The furnace was closed on top
with fire-brick slabs containing tivo or three holes for the
escape of the gaseous products of the reduction, and the whole
furnace was made air-tight by luting with fire-clay. Within a
few minutes after starting the dynamo, a stream of carbonic
oxide issued through the openings, burning usually with a flame
REDUCTION OF ALUMINIUM COMPOUNDS. 33 1
eighteen inches high. The time required for complete reduc-
tion was ordinarily about an hour. Experience has already
shown that aluminium, silicon, boron, manganese, sodium and
potassium can be reduced from their oxides with ease. In fact,
there is no oxide that can withstand the temperature attainable
in this furnace. Charcoal is changed to graphite; does this
indicate fusion? As to what can be accomplished by convert-
ing enormous electrical energy into heat within narrow limits,
it can only be said that it opens the way into an extensive field
of pure and applied chemistry. It is not difficult to conceive
of temperature limited only by the power of carbon to resist
fusion.
" Since the motive power is the chief expense in accomplish-
ing reductions by this method, its commercial success is
closely connected with obtaining power cheaply. Realizing
the importance of this point, Messrs. Cowles have purchased at
Lockport, N. Y., a water-power where they can utilize I200
horse-power. An important feature in the use of these furnaces
from a commercial standpoint is the slight technical skill re-
quired in their manipulation. The four furnaces operated in
the experimental laboratory at Cleveland are in charge of two
young men, who six months ago knew absolutely nothing
of electricity. The products at present manufactured are
the various grades of aluminium bronze, made from a rich
furnace product obtained by adding copper to the charge of
ore. Aluminium silver is also made ; and a boron bronze may
be prepared by the reduction of boracic acid in contact with
copper, while silicon bronze is made by reducing silica in con-
tact with copper. As commercial results may be mentioned
the production in the experimental laboratory, which averages
50 lbs. of 10 per cent, aluminium bronze daily, which can be
supplied to the trade in large quantities on the basis of $5 per
lb. for the aluminium contained, the lowest market quotation of
aluminium being now $15 per lb."
Dr. Hunt stated further that if the mixture consisted of alu-
mina and carbon only, the reduced metal volatilized, part es-
332 ALUMINIUM.
caping into the air and burning to alumina, part condensing in
the upper layer of charcoal, affording thus crystalline masses of
nearly pure aluminium and yellow crystals supposed to be a
compound of aluminium with carbon. Great loss was met in
collecting this divided metal into an ingot, so that only small
quantities were really obtained. To gather all the aluminium
together, a metal such as copper was added, thus producing an
alloy with 15 to 20 per cent, of aluminium ; on substituting
this alloy for pure copper in another operation, an alloy with
over 30 per cent, of aluminium was obtained.
Dr. Hunt, in a later paper,* stated that pure aluminium has
been obtained in this process by first producing in the furnace
an alloy of aluminium and tin, then melting this with lead,
when the latter takes up the tin and sinks with it beneath
the aluminium. He also stated that in the early experiments a
dynamo driven by a 30 horse-power engine yielded a daily out-
put of 50 lbs. of 10 per cent, aluminium bronze, but with a
larger machine the output was proportionally much greater.
In the latest practice, one-half cent per horse-power per hour
is said to cover the expense of working, making the 10 per
cent, bronze cost about 5 cents per lb. over the copper used.
Various shapes of furnaces have been used by the Cowles
Bros., the first described being a rectangular box, lined with
carbon, with the electrodes passing through the ends. Al-
though two other forms have been patented, we understand
that the kind now used, aad which is described at length in Mr.
Thompson's paper, is also of the oblong, horizontal style.
Chas. S. Bradley and Francis B. Crocker, of New York, patented
and assigned to the Cowles Electric Smelting Company,f the
use of a retort, composed of conducting material, surrounded
by a substance which is a poor conductor of heat, and having
inside a mixture of charcoal and the ore to be heated. Electric
connection being made with the ends of the retort, the walls of
♦National Academy of Science, Washington Meeting, April 30, 1886.
tU. S. Patent 335499, Feb. j., 1886.
REDUCTION OF ALUMINIUM COMPOUNDS. 333
the retort and the material in it are included in the circuit and
constitute the greater part of the resistance. The retort may
be stoppered at each end during the operation, and the heating
thus performed in a reducing atmosphere. Mr. A. H. Cowles
devised a style of furnace adapted for continuous working and
utilizing the full current of a dynamo of the largest size.f The
electrodes are tube-shaped and placed vertically. The positive
pole is above, and is surmounted by a funnel in which the
mixture for reduction is placed. The regular delivery of the
mixture is facilitated by a carbon rod, passing through the
cover of the funnel, which is serrated on the end and can be
worked up and down. The melted alloy produced, with any
slag, passes down through the negative electrode. The dis-
tance between the poles can be regulated by moving the upper
one, and the whole is inclosed in a fire-brick chamber. The
space between the electrodes and the walls is filled with an iso-
lating material, which is compact around the lower electrode
but coarse grained around the upper to facilitate the escape of
the gases produced. The chamber is tightly closed excepting
a small tube for the escape of gas.
A very complete description of the Cowles process was given
by Mr, W. P. Thompson (agent for the Cowles Co. in England)
in a paper read before the Liverpool Section of the Society of
Chemical Industry. f He describes the process as then carried
on in Lockport, the dynamo used being a large Brush machine
weighing 2J^ tons and consuming about lOO horse-power in
being driven at 900 revolutions per minute.
" Conduction of the current of the large dynamo to the furnace
and back is accompHshed by a complete metallic circuit, except
where it is broken by the interposition of the carbon electrodes
and the mass of pulverized carbon in which the reduction takes
place. The circuit is of 13 copper wires, each 0.3 inch in dia-
meter. There is likewise in the circuit an ampere meter, or am-
* English Patent 4664 (1887).
.f Journal of the Society of Chemical Industry, April 29, 1886.
334
ALUMINIUM.
meter, through whose helix the whole current flows, indicating
the total strength of the current being used. This is an import-
ant element in the management of the furnace, for, by the posi-
tion of the finger on the dial, the furnace attendant can tell to a
nicety what is being done by the current in the furnace. Be-
tween the ammeter and the furnace is a resistance coil of Ger-
man silver kept in water, throwing more or less resistance into
the circuit as desired. This is a safety appliance used in
changing the current from one furnace to another, or to choke
off the current before breaking it by a switch.
"The furnace (see Figs. 30, 31, 32) is simply a rectangular
Fig. 30.
box. A, one foot wide, five feet long inside, and fifteen inches
deep, made of fire-brick. From the opposite ends through the
pipes BB the two electrodes CC pass. The electrodes are im-
mense electric-light carbons three inches in diameter and thirty
Fig. 31.
LONGITUDINAL SECTION.
inches long. If larger electrodes are required, a series this size
must be used instead, as so far all attempts to make larger car-
bons that will not disintegrate on becoming incandescent have
failed. The ends of the carbons are placed within a few inches
REDUCTION OF ALUMINIUM COMPOUNDS.
335
of each other in the middle of the furnace, and the resistance
coil and ammeter are placed in the circuit. The ammeter regis-
ters 50 to 2000 amperes. These connections made, the furnace
is ready for charging.
" The walls of the furnace must first be protected, or the in-
tense heat would melt the fire-brick. The question arose, what
would be the best substance to line the walls. Finely powdered
charcoal is a poor conductor of electricity, is considered infusi-
ble and the best non-conductor of heat of all solids. From
these properties it would seem the best material. As long as
Fig. 32.
TRANSVERSE SECTION.
air is excluded it will not burn. But it is found that after using
pure charcoal a few times it becomes valueless ; it retains its
woody structure, as is shown in larger pieces, but is changed
to graphite, a good conductor of electricity, and thereby tends
to diffuse the current through the lining, heating it and the walls.
The fine charcoal is therefore washed in a solution of Hme-
water, and after drying each particle is insulated by a fine
coating of lime. The bottom of the furnace is now filled with
this lining about two or three inches deep. A sheet-iron gauge
is then placed along the sides of the electrodes, leaving about
two inches between them and the side walls, in which space
more of the charcoal is placed. The charge E, consisting of
about 25 pounds of alumina, iii its native form as corundum, 12
336 ALUMINIUM.
pounds of charcoal and carbon, and 50 pounds of granulated
copper, is now placed within the gauge and spread around the
electrodes to within a foot of each end of the furnace. For
making iron alloy where silicon also is not harmful, bauxite or
various clays containing iron and silica may be used instead of
the pure alumina or corundum. In place of granulated cop-
per, a series of short copper wires or bars can be placed parallel
to each other and transverse to the furnace, among the alumina
and carbon, it being found that where grains are used they
sometimes fuse together in such a way as to short-circuit the
current. After this, a bed of charcoal, F, the granules of which
vary in size from a chestnut to a hickory, is spread over all,
and the gauge drawn out. This coarse bed of charcoal above
the charge allows free escape of the carbonic oxide generated in
the reduction. The charge being in place, an iron top, G,
lined with fire-brick, is placed over the whole furnace and the
crevices luted to prevent access of air. The brick of the walls
insulate the cover from the current.
" Now that the furnace is charged, and the cover luted down,
it is started. The ends of the electrodes were in the beginning
placed close together, as shown in the longitudinal section, and
for this cause the internal resistance of the furnace may be too
low for the dynamo, and cause a short circuit. The operator,
therefore, puts sufficient resistance into the circuit, and by
watching the ammeter, and now and then moving one of the
electrodes out a trifle, he can prevent undue short-circuiting in
the beginning of the operation. In about ten minutes, the cop-
per between the electrodes has been melted and the latter are
moved far enough apart so that the current becomes steady.
The current is now increased till 1300 amperes are going
through, driven by 50 volts. Carbonic oxide has already com-
menced to escape through the two orifices in the top, where it
burns with a white flame. By slight movements outward of the
electrodes during the coming five hours, the internal resistance
in the furnace is kept constant, and at the same time all the
different parts of the charge are brought in turn into the zone
REDUCTION OF ALUMINIUM COMPOUNDS. 337
of reduction. At the close of the run the electrodes are in the
position shown in the plan, the furnace is shut down by placing
a resistance in the circuit, and then the current is switched into
another furnace charged in a similar manner. It is found that
the product is larger if the carbons are inclined at angles of 30°
to the horizontal plane, as in Fig. 33.
Fig. 33-
SECTION OF THE COWLES FURNACE.
" This regulating of the furnace by hand is rather costly and
unsatisfactory. Several experiments have therefore been tried
to make it self-regulating, and on January 26, 1886, a British
patent was applied for by Cowles Bros, covering an arrange-
ment for operating the electrodes by means of a shunt circuit,
electro-magnet, and vibrating armature. Moreover, if the elec-
trodes were drawn back and exposed to the air in their highly
heated state, they would be rapidly wasted away. To obviate
this, Messrs. Cowles placed what may be called a stufifiing-box
around them, consisting of a copper box filled with copper shot.
The wires are attached to the boxes instead of the electrodes.
The hot electrodes as they emerge from the furnace first en-
counter the shot, which rapidly carry off the heat, and by the
time they emerge from the box they are too cool to be oxidized
by contact with the air.
" Ninety horse-power have been pumped into the furnace for
five hours. At the beginning of the operation the copper first
melted in the centre of the furnace. There was no escape for
the heat continually generated, and the temperature increased
until the refractory corundum melted, and being surrounded on
all sides by carbon, gave up its oxygen. This oxygen, uniting
with the carbon to form carbonic oxide, has generated heat
338 ALUMINIUM.
which certainly aids in the process. The copper has had noth-
ing to do with the reaction, as it will take place in its absence.
Whether the reaction is due to the intense heat or to electric
action it is difficult to say. If it be electric, it is Messrs. Cowles'
impression that we have here a case where electrolysis can be
accomplished by an alternating current, although it has not
been tried as yet. Were the copper absent, the aluminium set
free would now absorb carbon, and become a yellow crystal-
line carbide of aluminium ; but, instead of that, the copper has
become a boiling, seething mass, and the bubblings of its vapors
may distinctly be heard. The vapors probably rise an inch or
two, condense, and fall back, carrying with them the freed alu-
minium. This continues until the current is taken ofif the fur-
nace, when we have the copper charged with 1 5 to 30 per cent.,
and in some cases as high as 40 per cent, of its weight of alu-
minium, and a little silicon. After cooling the furnace this
rich alloy is removed. A valuable property of the fine charcoal
is that the metal does not spread and run through the inter-
stices, but remains as a liquid mass, surrounded below and on
the sides by fine charcoal, which sustains it just as flour or
other fine dust will sustain drops of water for considerable
periods, without allowing them to sink in. The alloy is white
and brittle. This metal is then melted in an ordinary crucible
furnace, poured into large ingots, the amount of aluminium in
it determined by analysis, again melted, and the requisite
amount of copper added to make the bronze desired.
"Two runs produce in ten hours' average work 100 pounds
of white metal, from which it is estimated that Cowles Bros., at
Lockport are producing aluminium in its alloys at a cost of
about 40 cents per lb. The Cowles Company will shortly have
1200 horse-power furnaces. With a larger furnace there is no
reason why it should not be made to run continuously, like the
ordinary blast furnace.
" In place of the copper any non-volatile metal may be used
as a condenser to unite with any metal it may be desired to
reduce, provided, of course, that the two metals are of such a
REDUCTION OF ALUMINIUM COMPOUNDS. 339
nature that they will unite at this high temperature. In this
way aluminium may be alloyed with iron, nickel, silver, tin or
cobalt. Messrs. Cowles have made alloys containing 50 alu-
minium to 50 of iron, 30 aluminium to 70 of copper, and 25
aluminium to 75 of nickel. Silicon or boron or other rare
metals may be combined in the same way, or tertiary alloys
may be produced ; as, for instance, where fire- clay is reduced
in presence of copper we obtain an alloy of aluminium, silicon
and copper."
Soon after Mr. Thompson's description, the plant at Lock-
port was increased by the addition of the largest dynamo up to
that time constructed, built by the Brush Electric Company,
and dubbed the " Colossus." This machine weighs almost ten
tons, and when driven at 423 revolutions per minute it pro-
duced a useful current of 3400 amperes at a tension of 68 volts,
or at 405 revolutions produced a current of 3200 amperes with
83 volts electro-motive force, indicating 249,000 Watts or 334
electric horse-power. The steam engine was, in the latter case,
developing nearly 400 horse-power, and could not supply
more ; it was judged that the dynamo could have been driven
to 300,000 Watts with safety. The first run with this machine
was made in September, 1886. The furnaces used for this cur-
rent are of the same style as that described by Mr. Thompson,
but are larger, the charge being 60 lbs. of corundum, 60 lbs. of
granulated copper, 30 lbs. of coarse charcoal besides the pulver-
ized lime-coated charcoal used in packing. The operation of
reducing this charge takes about two hours. As soon as the
operation is finished the current is switched off into another
furnace prepared and charged, so that the dynamo is kept work-
ing continuously. In 1888, the Cowles Company had two of
these large dynamos in operation, and eight furnaces in use.
With two-hour runs a furnace is tapped every hour, producing
about 80 lbs. of bronze averaging 18 per cent, of aluminium.
The capacity of the plant is, therefore, about i}i tons of 10
per cent, bronze per day. Their alloys were sold in 1890 on
the basis of $2.50 per lb. for the contained aluminium.
340
ALUMINIUM.
The Cowles Syndicate Company, of England, located at
Stoke-on-Trent, have set up a large plant at Milton, where, pro-
fiting by the experience of the parent concern in America, still
larger electric currents are used, these being found more eco-
nomical. The dynamo in use at this works was built by Cromp-
ton, and supplies a current of 5000-6000 amperes at 50 to 60
volts. There are two furnace-rooms, each containing six fur-
naces, aluminium and silicon bronze being produced in one
room, and ferro-aluminium in the other. The furnaces used
measure 60 by 20 by 36 inches, inside dimensions, and differ
from those previously shown by having the electrodes inclined
at an angle of about 30°. (See Figs. 33, 34). The electrodes
COWLES' ELECTRIC SMELTING FURNACES AT STOKE-ON-TRENT, ENGLAND.
used are formed by bundling together 9 carbon rods, each 2^^
inches in diameter, each electrode weighing 20 lbs. More re-
cently larger carbons have been obtained, 3 inches in diameter,
and an electrode formed of five of these weighs 36 lbs. The
furnace is charge^ as previously described.
The current is started at 3000 amperes, gradually increasing
to 5000 during the first half hour, and then keeping steady
until the run is ended, which is about one and a half hours
from starting. The product of each run is about 100 lbs. of
raw bronze containing 15 to 20 per cent, of aluminium. The
return is said to average i lb. of contained aluminium per 18
REDUCTION OF ALUMINIUM COMPOUNDS, 34I
electric horse-power hours, or ij^ lbs. per electric horse-
power per day. The works produce about 200 lbs. of alumin-
ium contained in alloys per day. The raw bronze is stacked
until several runs have accumulated, then a large batch is melted
at once in a reverberatory furnace, refined and diluted to the
proportion of aluminium required by adding pure copper.
The Cowles Company, both in England and America, pro-
duce six standard grades of bronze as follows :
'Special" A.
A
B
C
D
E
11
per
cent, of aluminium
10
( it
TA
it It
S-SV2
t ti
t it
i ti
Their ferro-aluminium is sold with usually 5 to 7 per cent.
of aluminium, but 10, 13, and 15 per cent, is furnished if
asked for.
Products of the Cowles furnace. — Dr. W.. Hampe obtained the
following results on analyzing a sample of Cowles Bros.' 10 per
cent, bronze :
Copper 90.058
Aluminium 8.236
Silicon 1.596
Carbon. 0.104
Magnesium 0.019
Iron trace.
100.013
A sample of 10 per cent, bronze, made in the early part of
1886, and analyzed in the laboratory of the Stevens Institute,
showed —
Copper 88.0
Aluminium 6.3
Silicon 6.5
but it is evident that the percentage of silicon has since then
been lowered.
342 ALUMINIUM.
The ferro-aluminium used by Mr. Keep in his tests on cast-
iron was furnished by the Cowles Company, and analyzed —
Aluminium I ^4^
Silicon , 3'86
A sample shipped to England in December, 1886, contained —
Iron 86.69
Combined carbon I.oi
Graphitic carbon 1.9'
Total 2.92
Silicon 2.40
Manganese 0.31
Aluminium 6.50
Copper 1.05
Sulphur 0.00
Phosphorus 0.13
85.46
86.04
86.00
84.00
8.65
9.00
9.25
10.50
2.20
2.52
2.3s
2.40
3-77
2.41
2.50
The copper in this alloy was present by accident, the alloy
regularly made containing none, but the rest of the analysis
gives a correct idea of the constitution of the alloy. Prof.
Mabery gives several analyses of Cowles' ferro-aluminium : — *
Iron 85.17
Aluminium 8.02
Silicon 2.36
Carbon
The slags formed in the furnace in producing this alloy were
analyzed as follows : —
Silica 0.78 4.10
Alumina (insoluble) 0.20 —
Lime 28.50 14.00
Iron 1.50 29.16
Alumina (soluble) -(- aluminium 38.00 48.70
Sulphur 0.50 —
Graphite 5.00 2.60
Combined carbon 0.90 0.48
The slags formed when producing bronze vary in composition,
"American Chemical Journal, 1887, p. 11.
REDUCTION OF ALUMINIUM COMPOUNDS. 343
and are usually crystalline, with a shining, vitreous lustre.
Their analysis shows —
Alumina (insoluble) 55.30 66.84 —
Alumina (soluble) + aluminium 21.80 14.20 —
Lime 3.70 1.44 6.77
Copper — 3.32 i.oo
Carbon 0.65
The lime present probably existed as calcium aluminate. These
slags contained only a small amount of aluminium, rarely any
iron, and were usually free from silica.
The same chemist analyzed a peculiar product sometimes
formed in the furnace when smelting for bronze, in the shape
of crystalline masses, steel-gray to bright yellow in color, semi-
transparent and with a resinous lustre. These all contained
aluminium, copper, silicon and calcium in various proportions,
and when exposed to the air fell to powder. Analyses gave
Copper 26.70 35-0° 20.00 —
Aluminium 66.20 53-30 74.32 15.23
Silicon 5.00 12.30 2.86 20.55
Calcium 2.00 0.20 2.86 ^
Tin _ _ _ 49.26
99.90 100.80 100.04 85.04
The latter product was formed in smelting for aluminium-tin.
Prof. Mabery also found that the soot collecting at the ori-
fices on top of the furnace contained 10 to 12 per cent, of alu-
minium ; also that when alumina and carbon alone were heated
and silica was present, the aluminium formed dissolved up to
10 per cent, of silicon, which, on dissolving the aluminium in
hydrochloric acid, was left as crystalline or graphitic silicon.
Reactions in Cowles' process. — The inventors, themselves,
claim " reduction in a furnace heated by electricity in presence
of carbon and a metal." In their first pamphlet they say that
" the Cowles process accomplishes the reduction of alumina by
carbon and heat." Professor Mabery and Dr. Hunt, already
344 ALUMINIUM.
quoted, and Dr. Kosman * look at the process in no other light
than that the electric current is utilized simply by its conver-
sion into heat by the resistance offered, and that pure elec-
trolysis is either absent or occurs to so small an extent as to be
inappreciable. Indeed, if we consider the arrangement of the
parts in the Cowles furnace we see every effort made to oppose
a uniform, high resistance to the passage of the current and so
convert its energy into heat, and an entire absence of any of
the usual arrangements for electrolysis. For instance, elec-
trolysis requires a fluid bath in circulation, so that each ele-
ment of the electrolyte may be continuously liberated at one of
the poles and the presence of any foreign material, as bits of
carbon, between the poles is to be avoided if possible, since
they short-circuit the current and hinder electrolysis proper.
I think the arrangement of the furnace shows no attempt to
fulfil any of the usual conditions for electrolysis, but is one of
the best arrangements for converting the energy of the current
entirely into heat. Dr. Hampe, however, in spite of these
evident facts, draws the conclusion that because he was unable
to reduce alumina by carbon in presence of copper at the tem-
perature of a Deville lime-furnace, that it was therefore to be
assumed that even the somewhat higher temperature of the
electric furnace alone would be insufficient to accomplish the
desired reaction, and hence the effect of the electric arc must
be not only electro-thermic in supplying heat, but afterwards
electrolytic, in decomposing the fused alumina.
If we figure out the useful effect of the current, i. e., the pro-
portion of its energy utilized for the purpose of reducing alumina,
we find a low figure ; but it is well to note that although the
power required is one of the main features of this way of reduction,
yet this item is so cheap at the firm's works that it becomes a
secondary consideration in the economy of the process. A 300
horse-power current is equivalent to an expenditure of
300 7 — ?__ jg J 000 calories of heat per hour. Theoretically,
424
* Stahl und Eisen, Jan. I
REDUCTION OF ALUMINIUM COMPOUNDS. 345
this amount of heat would produce i^i^ = 261^ kilos or 58
pounds of aluminium. However, about 7 pounds are obtained
in an hour's working, which would show a useful effect of 12
per cent. This should even be diminished, since no account
has been taken of the combustion of carbon in the furnace to
carbonic oxide. The remainder of the heat account, probably
90 per cent, of the whole, is partly accounted for by the heat
contained in the gases escaping and the materials withdrawn
from the furnace (of which no resonable estimate can be made,
since the question of temperatures is so uncertain) and the
large remainder must be put down as lost by radiation and
conduction. As before remarked, water power is obtained by
this company very cheaply, and even this large loss does not
make much show in the cost of the alloy, yet the figures show
that a much larger useful effect should be possible, and it is not
at all improbable that the prospect of getting double or triple
the present output from the same plant is at present inciting
the managers to fresh exertions in utilizing the power to better
advantage.
Mr. H. T. Dagger's paper* on the Cowles process in Eng-
land, states that the product at their Milton works is i lb. of
aluminium to 18 electric horse-power per hour, which would
show that the dissociation of the alumina represented nearly 30
per cent, of the energy of the current ; but the data given in the
body of this gentleman's paper (p. 303 ) do not seem to indi-
cate so large a return as is stated above. Mr. Dagger, more-
over, maintains the purely electro-thermic action of the current,
denying that any electrolysis takes place at all, citing an ex-
periment with the alternating current in one of these furnaces,
which produced as much aluminium per horse-power as did the
direct current. In such an experiment electrolysis must neces-
sarily be absent.
In the discussion of Heroult's alloy process it will be shown
that in both it and Cowles' process the largest part of the re-
* British Association for Advancement of Science, Newcastle, 1889.
346 ALUMINIUM.
duction must necessarily be performed by chemical and not by
electrolytic action. I do not introduce this discussion here,
since the two processes resemble each other so closely in the
reaction involved that they can best be considered together.
Since 1892 no aluminium has been made in England by this
process, as the low price of pure aluminium killed the market
for ready-made aluminium alloys. I cannot say exactly to
what extent the Lockport works is running at the present time,
but it is probable that the death of one of the Cowles brothers
in 1893 and the sharp competition from pure aluminium have
seriously hampered the business of the American company.
At least, their products are not frequently seen on the market.
It may be proper to interject here mention of an unfortunate
occurrence in the history of the Cowles Company. They sold
only aluminium alloys until January, 1891, when they began
to advertise and sell pure aluminium made, it was said, by a
new process. The Pittsburgh Reduction Company working
the Hall process were then selling pure aluminium as low as
$1.50 per pound, while the Cowles Company commenced sell-
ing as cheap as $1.00. Inside of two months the Pittsburgh
Reduction Company instituted suit for infringement of the
Hall patents, asking the courts meanwhile for a preliminary
injunction. Judge Ricks, of Ohio, denied a complete injunc-
tion, but restrained the defendants from increasing the output
of their plant during the trial of the suit, or from selling alu-
minium below a price to be named by the complainants. The
latter named $1.50 per pound, and this fixed the market price
for some months. Several metallurgical experts of wide repu-
tation were engaged by both sides, and very voluminous testi-
mony was taken. While the suit was pending, the price of
aluminium was reduced by the European makers to 5 marks a
kilo (56 cents a pound), at which price important quantities
began to be imported, and the domestic makers could sell very
Httle at $1.50. In consequence, the Pittsburgh Reduction
Company notified the court that it would sell as low as $0.50
per pound. At this price, which was very nearly the cost of
REDUCTION OF ALUMINIUM COMPOUNDS. 347
production, aluminium continued until the suit was finally de-
cided, in February, 1893, in favor of the Hall process. Judges
Taft and Ricks decided that the Cowles Company were using
the Hall process when they electrolyzed a bath of molten
cryolite in which alumina was dissolved, and they were ordered
to stop the infringement and to pay the damages which it
might be estimated that their infringement had caused the
complainants' business.
Menges' Patent.
* This inventor proposes to produce aluminium or aluminium
bronze by mixing aluminous material with suitable conducting
material, such as coal, and a cohesive material, then pressing
into cylinders and baking hard. These strong, compact bars
conduct electricity, and are to be used like the carbon elec-
trodes of electric lamps in a suitably inclosed space.
Farmer's Patent.
M. G. Farmer f mixes aluminous material with molasses or
pitch, making a paste which is moulded into sticks, burned,
and used as electrodes, inclosed in a furnace. Aluminium is
produced by the arc, and drops into a crucible placed imme-
diately beneath.
Several other persons have patented exactly the same
method of procedure as that indicated by Menges and Farmer,
with the modification in some cases of mixing iron or copper
turnings with the aluminous material, and having the melted
material drop into a furnace kept hot by burning ordinary fuel.
Such a method of reducing refractory ores was even suggested
as far back as 1853. None of such processes are likely to give
results sufficiently economical for commercial use.
Kleiner's Process (1886).
This was devised by Dr. Ed. Kleiner of Zurich, Switzerland,
* German Patent, 40354 (1887).
t English Patent, 10815, Aug. 6, 1887.
348 ALUMINIUM.
and was patented in most of the European States. The Eng-
lish patent is dated 1886.* The first attempts to operate it
were at the Rhine Falls, Schaffhausen, and were promising
enough to induce Messrs. J. G. Nethers, Sons & Co., pro-
prietors of an iron works there, to try to obtain water rights for
1500 horse power, announcing that a company (the Kleiner
Gesellschaft) with a capital of 12,000,000 francs, was prepared
to undertake the enterprise and build large works. The pro-
position is said to have met with strong opposition from the
hotel-keepers and those interested in the falls as an attraction
for tourists, and the government declined the grant, consider-
ing that the picturesqueness of the falls would be seriously
afifected. This is the reason given by those interested in the
process for its not being carried out in Switzerland, it being
then determined to start a works in some part of England
where cheap coal could be obtained, and test the process on a
large scale. A small experimental plant was then set up in the
early part of 1887 on Farrington Road, London, where it was
inspected by many scientific men, among them Dr. John Hop-
kinson, F. R. S., who reported on the quantitative results
obtained ; a description of the process as here operated was
also written up for " Engineering." With the co-operation of
Major Ricarde-Seaver a larger plant was put up at Hope Mills,
Tydesley, in Lancashire, where the process was inspected and
reported on by Dr. George Gore, the electrician. After his
report we learn that the patents were acquired by the Alumin-
ium Syndicate, Limited, of London, a combination of capitalists
among whom are said to be the Rothschilds.
The aluminium compound used is commercial cryolite. It
is stated that the native mineral from Greenland contains on an
average, according to Dr. Kleiner's analysis, 96 per cent, of
pure cryolite, the remainder being moisture, silica, oxides of
iron and manganese. As pure cryolite contains 13 per cent,
of aluminium, the native mineral will contain 12^ per cent.,
♦English Patents, 8531, June 29, 1886, and 15322, Nov. 24, 1886.
REDUCTION OF ALUMINIUM COMPOUNDS.
349
all of which Dr. Kleiner claims to be able to extract. It is
further remarked that as soon as sufificient demand arises, an
artificial cryolite can be made at much less cost than that of the
native mineral, which now sells at ;^i8 to ;^20 a ton. The
rationale of the process consists in applying the electric current
in such a way that a small quantity of it generates heat and
keeps the electrolyte in fusion, while the larger quantity acts
electrolytically. Dry, powdered cryolite is packed around and
between carbon electrodes in a bauxite-lined iron crucible ; on
Fig. 35.
passing a current of high tension (80 to 100 volts) through the
electrodes, the cryolite is quickly fused by the heat of the arc
and becomes a conductor. As soon as the electrolyte is in
good fusion the tension is lowered to 50 volts, the quantity
being about 150 amperes, the arc ceases and the decomposi-
tion proceeds regularly for two or three hours until the bath is
35°
ALUMINIUM.
nearly exhausted. The evolved fluorine is said to attack the
bauxite, and by thus supplying aluminium to the bath extends
the time of an operation. In the first patent the negative car-
bon was inserted through the bottom of the melting cavity, the
positive dipping into the bath from above, (Fig. 35) but it was
found that while the ends of the positive carbon immersed in
the cryolite were unattacked, the part immediately over the
bath was rapidly corroded. In the second patent, therefore,
the positive electrode was circular and entirely immersed in
the cryolite, connection being made by ears which projected
through the side of the vessel. (Fig. 36.) As the carbons
Fig. 36.
are thus fixed, the preliminary fusion is accomplished by a
movable carbon rod suspended from above, passing through
the circular anode and used only for this purpose. The bath
being well fused and the current flowing freely between the
fixed carbons, the rod is withdrawn. The carbons are said to
be thus perfectly protected from corrosion, and able to serve
almost indefinitely. The melting pots finally used were or-
dinary black-lead crucibles, which are not usually injured at all,
since the fused part of the cryolite does not touch them, and
they last as many as 300 fusions. After the operation, the
carbons are lifted out of the bath and the contents cooled.
REDUCTION OF ALUMINIUM COMPOUNDS. 35 I
When solid, the crucibles are inverted and the contents fall
out. This residue is broken to coarse powder, the nodules of
aluminium picked out, melted in a crucible and cast into bars.
The coarse powder is then ground to fine dust. This powder
is more or less alkaline and contains a greater or less excess of
fluoride of sodium in proportion to the amount of aluminium
which has been taken out. If only a small proportion of the
metal has been extracted and the powder contains only a small
excess of sodium fluoride, it is used again without any pre-
paration in charging the crucibles ; but if as much as 5 or 6
per cent, of aluminium has been removed and the powder,
therefore, contains a large excess of sodium fluoride, it is
washed with water for a long time to remove that salt, which
slowly dissolves. The solution is reserved, while the powder
remaining is unchanged cryolite, and is used over. Dr. Gore
states that if the powder, electrodes and crucible are perfectly
dry, there is no escape of gas or vapor during the process ;
but if moisture is present, a small amount only of fumes of
hydrofluoric acid appear, and that there is no escape of fluorine
gas at any time. Dr. Kleiner hopes to soon dispense with the
interruption of the process, washing, etc., by regenerating
cryoHte in the crucible itself and so making the process con-
tinuous. One of the great advantages claimed is that the
aluminium is obtained in nodules, and not in fine powder; if it
was, it could not all be collected because it is so light, some of
it would float upon the water during the washing process and
be lost, and even when collected it could not be dried and
melted without considerable loss.
It has been found impossible in practice to obtain all the
aluminium from a given quantity of cryolite in less than two
fusions, for the sodium fluoride collecting in the bath hinders
the production of the metal. The proportion extracted by a
single fusion depends upon its duration. In the operations at
Tydesley, a fusion lasting 24 hours separated only 2^ per
cent, of aluminium, whereas the cryolite contained 12^ per
cent. At this rate, to extract the whole in two operations would
352 ALUMINIUM.
require two fusions of 6o hours each. As to the output, on an
average a current of 38 electric horse-power deposited 150
grammes of aluminium per hour, being a little over 3 grammes
per horse-power. Since a current of 50 volts and 150 amperes,
such as was stated above as the current in each pot, is equal to
50x^50 ^^ j^ electric H. P., it is probable that the 38 H. P. cur-
rent mentioned must have been used for four crucibles. Now,
the output of four crucibles, each with a current of 150 amperes,
should have been 0.00009135X150X4=0.0548 gramme per
second, or 197.3 grammes per hour; the difference between
this and the amount actually obtained, or 47.3 grammes, is the
amount of aluminium which was produced and then afterwards
lost either as fine shot-metal or powder, or dissolved again by
corroding elements in the bath. To calculate how the output
of 3 grammes per electric H. P. per hour compares with the
quantity of metal which this amount of energy should be able
to produce, we can assume that since it takes at most 4 volts to
decompose the aluminium fluoride, the four crucibles would
consume 16 volts in decomposition, being sixteen-fiftieths of
the total voltage employed. Since the amperes only produced
150 grammes out of 197.3 theoretically possible, the efhciency
over all is only
16 150 1
As to the purity of the metal obtained, the process is met at
the outset by the silica and iron oxide in the cryolite, which are
probably all reduced with the first few grammes of aluminium
thrown down. This can possibly be remedied by using a purer
artificial cryolite ; the impurities cannot generally be separated
from the natural mineral. Then there are impurities of a simi-
lar nature coming from the carbons used, and which are gene-
rally present if especial pains are not taken to get very pure ma-
terials for making them. Dr. Kleiner's early attempts produced
metal of 85 to 95 per cent, purity, but he stated in 1889 that it
was uniformly 95 to 98 per cent., and being put on the market in
REDUCTION OF ALUMINIUM COMPOUNDS. 353
competition with other commercial brands. It appears, how-
ever, from a consideration of the preceding data, that the pro-
cess could not produce aluminium much cheaper than 12 shil-
lings a pound, and it was therefore abandoned in 1890. It may
be observed that the mechanical arrangements for carrying on
this process, as above outlined, could not stand comparison with
the present forms of apparatus in use by the Hall and Heroult
processes.
Lossier's Method.
* This is a device for decomposing the natural silicates by
electricity and obtaining their aluminium. The bath is com-
posed of pure aluminium fluoride or of a mixture of this salt
and an alkaline chloride, and is kept molten in a round bot-
tomed crucible placed in a furnace. The electrodes are of dense
carbon and are separated in the crucible by a partition reach-
ing beneath the surface of the bath. The positive electrode is
furnished with a jacket or thick coating of some aluminium sili-
cate plastered on moist and well dried before use. When the
current is passed, the aluminium fluoride yields up its fluorine at
this pole and its aluminium at the other. The fluorine com-
bines with the aluminium silicate, forming on the one hand alu-
minium fluoride, which regenerates the bath, on the other silicon
fluoride and carbonic oxide, which escape as gases. The metal
liberated at the negative pole is lighter than the fused bath, and
therefore rises to the surface.
M. Grabau cites as one of the recommendations of aluminium
fluoride for use in his process (p. 295), that it is quite infusible,
so it would appear that Lossier has made a mistake in suppos-
ing that it could be melted alone in a crucible. It would, how-
ever, make a very fusible bath when the alkali chloride was
added. It is probable that the carrying out of this method
would develop great trouble from the attacking of the crucible
by the very corrosive bath, the disintegration of the carbons,
which would cause much trouble at the negative pole especially,
* German Patent (D. R. P.), No. 31089.
23
354 ALUMINIUM.
and the oxidation of the fluid aluminium on the surface of the
bath. The process has never been attempted on a large scale,
and it is very unlikely that it ever will be.
OmhoKs Furnace.
I. Omholt and the firm Bottiger and Seidler, of Gossnitz, have
patented the following apparatus for the continuous electrolysis
of aluminium chloride:* —
The bed of a reverberatory furnace is divided by transverse
partitions into two compartments, in each of which are two re-
torts semi-circular in section, lying side by side horizontally
across the furnace, with the circular part up. They are sup-
ported on refractory pillars so that their open side is a small
distance above the floor of the furnace. The aluminium com-
pound being melted on the hearth, it stands to the same depth
in both retorts, and if the electrodes are passed through the
bottom of the hearth they may remain entirely submerged in
molten salt and each under its own retort cover. The metal
therefore collects in a liquid state under one retort and the
chlorine under the other, both being preserved from contact or
mixture with the furnace gases by the lock of molten salt. The
chlorine can thus be led away by a pipe, and utilized, while the
aluminium collects without loss, and is removed at convenient
intervals.
The great cost of making aluminium chloride will probably
prevent it ever being used again in the metallurgy of alumin-
ium, but the form of furnace described above may possibly be
utilized in operating the decomposition of some other aluminium
salt, such as the double sulphide with soda.
Minefs Process (1887).
This consists, according to the patent specification, f in the
electrolysis of a mixture of sodium chloride with aluminium
fluoride or with the separate or double fluorides of aluminium
* German Patent (D. R. P.), No. 34728.
t English Patent, No. 10057, July r8, 1887.
REDUCTION OF ALUMINIUM COMPOUNDS. 355
1
and sodium, melted in a non-metallic crucible or in a metallic
one inclosed in a thin refractory jacket to avoid filtration, the
aluminium fluoride decomposed being regenerated by causing
the fluorine vapors evolved to act on bauxite or alumina
placed somewhere about the anode. The details of the appar-
atus and bath are as follows : —
Disposition of the Apparatus. — The pots or crucibles used
may be of refractory earth, plumbago, or of metal, and in cases
where an alloy is required the crucible itself serves as an elec-
trode. None of these, however, resist the corrosive power of
the electrolyte and would under ordinary conditions be quickly
destroyed. To overcome this difficulty two special devices are
employed. When alloys are to be made directly, the pot is
cast of the metal with which the aluminium is to be combined.
It is shaped with a sloping bottom and provided with a tap
hole. The pot is encased in thin brickwork and is then made
the negative electrode, the positive being two carbon rods
dipped into the bath. As soon as the current is passed alu-
minium is deposited on the walls of the pot, forming a rich
alloy with the metal of which the pot is made (iron or copper).
When this coating becomes sufficiently rich in aluminium, the
heat of the bath melts it and it trickles down and collects at the
bottom. After a certain time, the alloy can be tapped out
regularly at intervals without interrupting the electrolysis. The
metal thus obtained is principally aluminium containing a few
per cent, of the metal of the pot, which is of no consequence,
since the end to be finally attained is the production of an alloy
with a smaller quantity of aluminium. When pure aluminium is
to be obtained, an ingenious device is used to protect the metal
from contamination by the metal of the pot. Carbon plates, A
and C (Fig. 37), serve as anode and cathode, the cathode stand-
ing upright in a small crucible placed upon a plate resting on
the bottom of the pot. This crucible and plate are made from
'carbon blocks or from fused alumina or fluorspar moulded into
the shape desired. As the metal is set free it trickles down
the cathode and is caught in the crucible or cup, thus being
356
ALUMINIUM.
prevented from spreading out over the bottom of the pot. To
prevent the bath from corroding the pot, the wire R is passed
from the latter to the negative pole of the circuit. The pot is
thus made part of the negative electrode, but it is not intended
that much of the current should pass through it, so a resistance
coil is interposed between it and the battery or dynamo, so that
Fig. 37.
the derived current passing through the sides of the pot is only
5 to 10 per cent, of the whole current. The effect of this is
that a small amount of aluminium is deposited on and alloys
with the sides of the vessel, which protects the latter from cor-
rosion and is only feebly acted upon by the bath. The metal
deposited in the crucible is thus kept nearly pure, while a small
amount of alloy falls to the bottom of the pot and is poured
out after the crucible has been removed. When it is wished to
obtain the purest aluminium, the intensity of the derived cur-
rent passing through the pot is increased by removing part of
the resistance interposed between it and the negative wire, thus
also decreasing the intensity of the principal current. The
REDUCTION OF ALUMINIUM COMPOUNDS. 357
nature of the electrodes proper may be varied. For producing
pure aluminium the anode is carbon, the cathode carbon, and
the pot either of copper or iron ; for producing copper alloys
the anode may be either carbon or bright copper, and the
cathode (pot) of carbon or copper; for producing iron alloys
the anode may be either carbon or iron, while the vessel used
as cathode is either of cast-iron or plumbago.
Composition and properties of the baths. — Minet has made
more careful electrical measurements on these fused baths than
any other metallurgist, a point of particular importance in his
experiments being the accurate measurement of the tempera-
tures by means of a Le Chatellier electric pyrometer. On this
account his result^re a valuable contribution to the knowledge
of the present electrolytic processes, and are therefore worth
repeating in extenso. Minet first experimented with a bath of
Aluminium-sodium chloride 40 parts.
Sodium chloride 60 "
He says of the working of this mixture that it gives rise to
abundant vapors, which are very disagreeable. In consequence,
the bath becomes quickly impoverished in aluminium chloride,
it becomes pasty, and can only be liquefied by raising the tem-
perature almost to the melting point of sodium chloride. It is
difficult under these conditions to produce regular and continu-
ous electrolysis.
Minet obtained much better results with aluminium fluoride.
He mixed cryolite with common salt in the following propor-
tions :
Cryolite 37-5 parts.
Sodium chloride 62.5 "
giving a mixture whose formula would be AlFgSNaF + 6NaCl.
This mixture has the following properties :
Melting point 675° C.
Vapors given off at 1056° C.
Specific gravity at 829° C 1.76
Specific resistance at 870° C 0.32 ohms.
3S8 ALUMINIUM.
The last datum means that a column of the electrolyte i
centimetre square and i centimetre long would give 0.32 ohms
resistance to the passage of the current. If the section of the
electrolyte through which the current passed averaged 750
square centimetres, and the electrodes averaged 6 centimetres
apart, the total resistance of the bath would be
0.32 X ^0.0026 ohms:
750
and if the current was 1 500 amperes, the voltage absorbed by
the electrical conduction-resistance of the bath would be
0.0026 X 1500 = 3.9 volts.
The specific resistance was found to decrease about 0.07 per
cent, for every degree rise of temperature above 870°, or 7 per
cent, for every lOO degrees.
If this bath were simply electrolyzed, fluorine would be dis-
engaged, escaping into the air as carbon fluoride, CF4, while
the bath would become poorer in aluminium fluoride. If cryo-
lite alone were added during the process, sodium fluoride would
accumulate in the bath, and after a certain time sodium would
be set free. If the bath is renewed by adding aluminium fluor-
ide, this inconvenience is obviated, but there still remains the
question of suppressing the noxious fluoride vapors set free. If
the bath is renewed by placing alumina in the state of fine pow-
der in the bath, dropping it especially around the anode, the
fluorine set free may reform aluminium fluoride by attacking
the alumina, setting free oxygen, which combines with the car-
bon anode to form carbonic oxide. If the fluorine were not
completely absorbed by the alumina, the amount escaping would
have to be made up for by adding aluminium fluoride to the
bath. The bath should therefore be fed by both alumina and
aluminium fluoride.
The above contains Minet's views of what takes place when
alumina is added to the fluoride bath. He does not admit that
any alumina can be really dissolved in the bath and be electro-
REDUCTION OF ALUMINIUM COMPOUNDS. 359
lyzed as alumina (the view taken by Hall). Minet, in fact,
maintains that when alumina is added to molten cryolite it
sinks through it and remains undissolved, as, for instance, very
fine marble dust would in water. Such, however, is not the
experience of other investigators. According to numerous
experiments by Hall and others using the present electrolytic
processes, as well as some made by the writer, finely-divided
alumina appears to dissolve in molten cryolite exactly as sugar
does in water, and there is even a saturation point, at about 30
per cent., above which no more dissolves. The bath containing
alumina forms to all appearances a homogeneous liquid.
Driven from their first position, the adherents to Minet's views,
having allowed that a homogeneous liquid bath does result, as-
sert that the alumina is only mechanically suspended, like
clay in muddy water, and that in this condition it is carried to
the anode and unites with the fluorine set free. Such a view,
however, is also erroneous, because regeneration in such a man-
ner could not be anything like complete, and considerable
amounts of fluorine would escape ; yet in the Hall process,
when the operation is properly conducted, not a trace of fluoride
gas escapes. Regeneration by mechanically-suspended alu-
mina could not possibly be so complete.
We shall continue describing Minet's experiments, asking that
it be remembered, however, that we regard as erroneous his
view that aluminium fluoride is the substance immediately de-
composed by the current when alumina is present.
Taking the bath already described, with electrodes of such
size and distance apart that the conduction-resistance at 900°
was 0.0044 ohms, the following results were obtained : —
Temperature.
Electromotive force
Conduction-resistance
for decomposition.
of the bath.
900°
2.4 volts
.0044 ohms
1000°
2.34 "
.0033 "
1100°
2.17 "
.0025 "
If V' = the voltage required for decomposition,
V° = the voltage required for conduction,
V = the total voltage absorbed by the bath,
A =; the amperage of the current.
then [V = VI -(- AV".]
36o
ALUMINIUM.
We can thus calculate the voltage required to send through
this bath any number of amperes at a given temperature.
Thus, for lOO or looo amperes the voltage absorbed per bath
would be as follows :
Temperature. Amperes. Voltage for
decomposition.
900"
I0CX3°
1 100"
100
2.4
1000
2.4
100
2.34
1000
2-34
100
2.17
1000
2.17
iltage for
Total
Per cent, of total
aduction
iistance.
voltage.
voltage absorbed
in conduction re-
sistance.
0.44
2.88
«5
4.40
6.80
65
0-33
2.67
12
3-30
5.64
59
0.25
2.42
13
2.50
4.67
54
It thus appears that, using a bath of a given size, the voltage
required to send lOOO amperes through it is only 2 to 2.5 times
that required for 100 amperes. Since the power required is
just in the same ratio, it follows that it is economical to send as
large a current as practicable through a bath of a given size.
The last column shows us the percentage of the energy of the
current which will be converted into heat. It follows from
these figures that the heating effect of the current increases
very rapidly with its quantity, so that a given number of
amperes will supply enough heat to keep the bath molten with-
out exterior heat; more than this number would, in fact, raise
the temperature of the bath too high, and this limits the size of
the current which it is practicable to send through a bath of a
given size.
Minet also found that when such a bath contained salts of
iron and silicon, which are weaker compounds than aluminium
or sodium salts, a current of carefully regulated low voltage, and
consequently of low density, would first separate these com-
pletely. An experiment made with a bath in which the anode
surface was 500 square centimetres, and gradually increasing
the voltage, gave the following successive results :
REDUCTION OF ALUMINIUM COMPOUNDS. 36 1
Total Amperes Amperes per Electro-motive Nature of the
voltage passing. sq. c. m. of force of decom- metal deposited.
used.
anode.
position (volts).
I.2I
75
o.is
0.54
Iron.
1.68
100
0.20
0.7s
Iron ( traces of silicon) .
2.48
125
0.25
1-37
Ferro-silicon.
2.89
150
0.30
1.54
Ferro-silicon (traces of aluminium)
2.94
15°
0.30
1.74
Silicon-aluminium (traces of iron) .
4.27
250
0.50
2.IS
Aluminium (traces of silicon) .
6.85
500
1. 00
2.50
Aluminium (traces of sodium).
The conduction-resistance of the bath remained very nearly
constant throughout.
In a large number of experiments, the amount of metal actu-
ally obtained was 50 to 80 per cent, of the amount which
the amperage of the current could theoretically produce, on an
average about 60 per cent. As for the power required, an
experiment lasting 24 hours, at a temperature of 1 160°, voltage
5.75, and amperes 1500, showed 21.5 grammes of aluminium
deposited per hour per electric horse-power used. Another
similar experiment, but with the electrodes closer together, the
voltage consequently less, and at a lower temperature, gave 31.9
grammes per horse-power-hour, which would be 0.765 kilos
(1.685 pounds) per electric horse-power per day. As the en-
ergy of one horse-power-day is equivalent to the energy of oxi-
dation of 2.1 kilos (4.63 pounds) of aluminium, the useful efifect
over all is 36.5 per cent.
Quality of metal. — When working for pure aluminium, about
three-fourths of the metal produced is taken from the crucible
in which the cathode stands, and is 98 to 99 per cent, pure ;
the other one-fourth has been deposited on the sides of the
cast-iron pot, and contains 10 to 20 per cent, of iron. It is
poured out and used for making ferro-aluminium.
Installations of the process. — Minet conducted his work at the
expense of Messrs. Bernard Bros. The first experiments were
made on the road Moulin Joli, in Paris, from March, 1887, to
March, 1888. This plant consisted of a 6 horse-power engine
and a Gramme dynamo capable of giving a current of 250
amperes at 12 volts tension. In the year named, this plant pro-
362 ALUMINIUM.
duced about 500 kilogrammes of pure aluminium and 1500
kilogrammes of ferro-aluminium or aluminium bronze.
The second installation was put up at Creil (Oise), com-
menced operations in April, 1888, and continued working until
October, 1891. This plant had a 40 horse-power engine, and
an Edison dynamo giving a current of 1200 amperes and 27.5
volts. Regularly it was run at only 16 volts, operating three
baths in tension, and at looo amperes. There were made here
daily about 10 kilos of pure aluminium and 5 to 6 kilos of alu-
minium in alloys.
At the first location, Minet was enabled to study experiment-
ally the purely scientific part of his processes ; the plant at
Creil enabled him to solve the practical details of the process.
In 1889, the Messrs. Bernard Bros, determined to work the
process on a large, industrial scale, and cast around for a loca-
tion having abundant water-power. It was decided to locate at
Saint Michel in Savoy. The stream utihzed is the Valoirette,
giving a volume of 3.5 cubic metres per second with a fall of
133 metres. This gives theoretically 6000 horse-power, and
should produce 4000 electric horse-power.
At this place were put up a turbine of 300 horse-power by
Bouvier of Grenoble, and a dynamo of 275 horse-power by
Hillairet-Huguet of Paris. The latter gives a current of 4000
amperes at 50 volts tension, aiid produces regularly about 150
kilos (330 pounds) of aluminium. It is stated that a 600 horse-
power dynamo, actuated by a lOOO horse-power turbine, was
started during 1894. Latest advices state that this estabUsh-
ment has been acquired by a French company formed to work
under the Hall patents.
Feldman's Method (1887).
A. Feldman, of Linden, Hannover, patented the following
electrolytic process : * —
A double fluoride of aluminium and an alkaline earth metal,
* English Patent, No. 12575, Sept. 16, 1887.
REDUCTION OF ALUMINIUM COMPOUNDS. 363
mixed with an excess of a chloride of the latter group, is either
electrolyzed or reduced by sodium. The proportions of these
substances to be used are such as take place in the following
reactions : —
1. (AUF6+2SrF2) + 6SrCI.,=2Al+5SrF2+3SrCl2+6Cl.
2. (AljF6+2SrF2)+6SrCl2+6Na=2AH-sSrF2+3SrCl2+6NaCl.
The three equivalents of strontium chloride are found in prac-
tice to be most suitable. Potassium chloride may also be
added to increase the fluidity, but in this case the strontium
chloride must be in still greater excess.
Even if the above reactions and transpositions do take place,
the use of so much costly strontium salts would appear to ren-
der the process uneconomical.
Warren's Experiments (1887).
Mr. H. Warren, of the Everton Research Laboratory, has
outlined the following methods or suggestions, some of which
had already been carried out, and probably others have since
given useful ideas to workers in this line. The principle can
hardly be called new, since suggestions almost identical with
Mr. Warren's were made previously to his, but the latter's re-
sults are the first recorded in this particular direction:* "This
method of preparing alloys differs only slightly from the man-
ner in which amalgams of different metals are prepared, substi-
tuting for mercury the metals iron, copper, or zinc made liquid
by heat. These metals are melted, connected with the negative
pole of a battery, and the positive pole immersed in a bath of
molten salt floating on top of the melted metal. The apparatus
used is a deep, conical crucible, through the bottom of which
is inserted a graphite rod, projecting about one inch within, the
part outside being protected by an iron tube coated with borax.
As an example of the method, to prepare silicon bronze, copper
is melted in the crucible, a bath of potassium silico-fluoride is
* Chemical News, Oct. 7, 1887.
364 ALUMINIUM.
fused on top to a depth of about two inches. A thick platinum
wire dips into this salt, and on passing the electric current an
instantaneous action is seen, dense white vapors are evolved,
and all the silicon, as it is produced, unites with the copper,
forming a brittle alloy. Cryolite may be decomposed in like
manner if melted over zinc, forming an alloy of zinc and alu-
minium, from which the zinc can be distilled, leaving pure
aluminium."
Mr. Warren does not affirm that he has actually performed
the decomposition of cryolite in the way recommended, but
states that it may be done ; from which we would infer that he
simply supposed it could. A well-recorded experiment, then,
is needed to establish the truth of this statement. Neither does
he propose to make aluminium bronze in this way; it may be
that it was attempted and did not succeed, for Hampe states
that an experiment thus conducted did not furnish him alu-
minium bronze (p. 368).
Zdziarski' s Patent.
A. Zdziarski,* of Brest-Litowsk, Russia, appears to have
patented the above principle in 1884, for in his patent he states
that the metal to be alloyed with aluminium is melted in a
crucible, covered with a fusible compound of aluminium for a
flux (alumina and potassium carbonate may be used) and made
the negative pole of an electric current, the positive pole being
a carbon rod dipping in the flux.
Grabau's Apparatus.
LudwigGrabaUjf of Hannover, Germany, proposes to electro-
lyze a molten bath of cryolite mixed with sodium chloride. The
features of the apparatus used are an iron pot, in which the
bath is melted, and water-cooled cylinders surrounding both
electrodes, the jacket surrounding the negative one having a
* English Patent 3090, Feb. 11, 1884.
t German Patent (D. R. P.), No. 45012.
REDUCTION OF ALUMINIUM COMPOUNDS. 365
bottom, the other not. The object of these cylinders is, at the
positive electrode, to keep the liberated fluorine from attacking
the iron pot and so contaminating the bath, at the other pole
the liberated aluminium is kept from dropping to the bottom
of the pot, where it might take up iron, and can be removed
from the bath by simply lifting out the water-cooled cylinders
and carbon electrode. Mr. Grabau states that he has abandoned
this process because the inseparable impurities in the cryolite
produced impurities in the metal; it may be that with the pure
artificial cryolite, which he makes by his other processes (see
p. 171), this electrolytic process may again be taken up. (See
also p. 294.)
Rogers' Process (1887).
In July, 1887, the American Aluminium Company, of Mil-
waukee, was incorporated, with a capital stock of $1,000,000,
for the purpose of extracting aluminium by methods devised
by Prof. A. J. Rogers, a professor of chemistry in that city.
This gentleman had been working at the subject for three or
four years previous to that time, but it has not been until re-
cently that patents have been applied for, and they are still
pending.
The principle made use of has already been suggested in con-
nection with the production of sodium (p. 219). It is briefly,
that if molten sodium chloride is electrolyzed, using a molten
lead cathode, a lead-sodium alloy is produced. This alloy is
capable of reacting on molten cryolite, setting free aluminium,
which does not combine with the lead remaining because of its
weak affinity for that metal. If, then, cryolite is placed in the
bath with the sodium chloride, the two reactions take place at
once, and aluminium is produced. In the early part of 1888,
the company erected a small experimental plant, with a ten-
horse-power engine, with which the following experiments,
among many others, were made: —
I. *A current of 60 to 80 amperes was passed for several
* Proceedings of the Wisconsin Nat. His. Soc, April, 1889.
366 ALUMINIUM.
hours through a bath of cryolite melted in a crucible lined with
alumina, and using carbon rods 2^ inches in diameter as
electrodes, one dipping into the bath from above, the other
passing through the bottom of the crucible into the bath.
Only I or 2 grammes of aluminium were obtained, showing
that the separated metal was almost all redissolved or reunited
with fluorine. With the temperature very high, it was found
that sodium passed away from the bath without reducing the
cryolite.
2. A current averaging 54 amperes and 10 volts was passed
for five and a half hours through a mixture of I part cryolite
and 5 parts sodium chloride placed in a crucible with 3 70
grammes of molten lead in the bottom as the cathode. After
the experiment, 25 grammes of aluminium were found in
globules on top of the lead-sodium alloy. This latter alloy
contained some aluminium. The globules were about as pure
as ordinary commercial aluminium, and contained no lead or
sodium. From another experiment it was determined that the
lead-sodium alloy must first acquire a certain richness in
sodium before it will part with any of that metal to perform
the reduction of the cryolite. It was also found that a certain
temperature was necessary in order that aluminium be pro-
diiced at all.
3. A current of 75 amperes and about 5 volts suflficed to de-
compose the bath and to produce 105 grammes of aluminium
in seven hours. This would be nearly 30 grammes per hour
for each electric horse-power.
4. A current of 80 amperes and 24 volts was passed through
four crucibles connected in series for six hours, using a bath
of I part cryolite and 3 parts sodium chloride with 450
grammes of lead in each crucible. The crucibles were heated
regularly to a moderate temperature. There were obtained
altogether 250 grammes of quite pure aluminium. This would
be equal to 16 grammes per electric horse-power-hour.
" A large number of similar experiments afforded a return of
^ to I ^ lbs. of aluminium per electric horse-power per day.
REDUCTION OF ALUMINIUM COMPOUNDS. 367
The experimental plant now in operation consists of a 40 volt
— TOO ampere — dynamo, the current being sent through six pots
connected in series. When the bath is completely electrolyzed
the contents of the crucible are tapped ofif at the bottom and a
fresh supply of melted salt poured in quickly. The lead-
sodium alloy run off is put back into the crucibles, thus keep-
ing approximately constant in composition and going the
rounds continuously. With this apparatus, 3 to 4 lbs. of alu-
minium are produced regularly per day of 12 hours. As soon
as patents are obtained, it is the intention of the company to
put up a plant of 50 lbs. daily capacity, which can be easily
increased to any extent desired as the business expands."
Professor Rogers observes in regard to the apparatus that he
has tried various basic linings for his clay crucibles, but a paste
of hydrated alumina, well fired, has succeeded best. Some
"shrunk" magnesia lining, such as is used in basic steel fur-
naces, answered well, but could not be used because of the
amount of iron in it. Lime could not be used, as it fluxed
readily. The carbon rods lasted 48 hours without much cor-
rosion if protected from the air during electrolysis. Carbon
plates and cylinders were tried, but the solid rods gave the
best results. About 8 to 10 per cent, of aluminium can be
extracted from cryolite containing 12.85 P^r cent. The min-
eral used was obtained from the Pennsylvania Salt Company,
and was called pure, but it contained 2 per cent, of silica and
I per cent, of iron. These impurities pass largely into the
aluminium produced, but the company hoped to be able to
manufacture an artificial aluminium fluoride which will not
only be purer but less costly than this commercial cryolite.
Professor Rogers infers that pure aluminium fluoride would not
be an electrolyte, since the resistance of the bath increases as
the amount of other salts present decreases.
It is useless to base any accurate estimation of the cost of
aluminium by this process on the data given above, since they
were only for a small experimental plant. If, however, 75 per
cent, of the aluminium in cryolite can be extracted at the rate
368 ALUMINIUM.
of I lb. of metal per day per electric horse-power, and the
metal is free from lead and sodium, (a sample sent me was
of very fair quality,) it would seem that the process was in a
fair way to compete on an equal footing with the other electro-
lytic processes as operated in 1889, but it has been entirely
distanced by more recent developments.
Dr. Hampe on the Electrolysis of Cryolite.
Prof. W. Hampe, of Clausthal, whose name is a guarantee of
careful and exact observations, has written the following val-
uable information on this subject, in presenting which we will
also give the remarks of Dr. O. Schmidt, called forth by
Hampe's first article.
*" The electrolysis of a bath of cryolite mixed with sodium
and potassium chlorides, using a layer of melted copper in the
bottom of the crucible as cathode and a carbon rod as anode,
gave balls of melted sodium which floated on the surface and
burnt, but scarcely a trace of aluminium. Yet here the condi-
tions were most favorable to the production of the bronze. The
battery used consisted of twelve large zinc-iron elements.''
fDr. O. Schmidt, referring to this statement of Hampe's,
quotes an opposite experience. He fused cryolite and sodium
chloride together in a well-brasqued crucible in the proportions
indicated by the reaction
AUF6.6NaF+6NaCl=Al2Cle+i 2NaF.
At a clear red heat the bath becomes perfectly fluid and trans-
parent, and an anode of gas carbon and a cathode of sheet cop-
per are introduced. On passing the current the copper did not
melt but became covered with a film of deposited aluminium,
which in part penetrated the electrode and in part adhered to
the surface as a rich alloy which ultimately fused ofif and sank
to the bottom of the crucible. With a plate i to i ^ millimetres
thick, 10 per cent of its weight of aluminium could thus be de-
* Ghemiker Zeitung, xii., 391 (1888). fldem, xii., 457 (i
REDUCTION OF ALUMINIUM COMPOUNDS. 369
posited ; with one 3 millimetres thick, about 5 per cent. The
metal could be made perfectly homogeneous by subsequent
fusion in a graphite crucible. Dr. Schmidt further remarks
(evidently on the supposition that the reaction he gives actually
takes place) that on thermo-chemical grounds sodium would not
here be reduced, because while the molecule of sodium chloride
requires 97.3 calories for its decomposition, that of aluminium
chloride, — ^, requires only 80.4, and the current would attack
first the most easily decomposed. He also states that the cal-
culated difference of potential for the dissociation of aluminium
chloride which is ^'^ = 3.5 volts, was actually observed, and the
tension of the current must have been increased to about 4.5
volts to bring about the decomposition of the sodium chloride.*
Dr. Hampe's statement occasioned several other communica-
tions, which he considers and replies to in the following
article : f —
" Dr. O (whose name I withhold at his own request)
writes to me that by electrolyzing pure cryolite, using a nega-
ative pole of molten copper, he never obtained aluminium
bronze ; but, on the other hand, always obtained it if he used
the mixture of cryolite and sodium chloride mentioned by Dr.
Schmidt, and in place of the molten copper a thick stick of the
unfused metal. A letter from R. Gratzel, Hannover, contains a
similar confirmation of the latter observation. By electrolyzing
a mixture of 100 parts cryolite with 150 of sodium chloride in
* Aside from Hampe's subsequent remarks as to no aluminium chloride being
formed, we would further point out the fact that the decomposition of a chemically
equivalent quantity of aluminium chloride requires not — ^ = 80.4 calories, but
^"' °° or 53.6 calories, and the calculated difference of potential is properly -^^
or 2.3 volts. The fact that the observed tension was 3.5 volts shows that the current
was not strong enough to decompose the sodium chloride, as Schmidt observes, and
the fact that this current deposited aluminium would show that the heat of formation
of aluminium fluoride at this temperature cannot be greater than 23X3.5X6^483
(thousand) calories.
tChemiker Zeitung (Cothen), xiii., 29 and 49.
24
370 ALUMINIUM.
a graphite crucible holding 30 kilogrammes, aluminium bronze
dripped down from the ring-shaped copper cathode used, while
chlorine was freely disengaged at the carbon anode. But after
a time, long before the complete decomposition of the cryolite,
the formation of bronze stopped — even an attacking of that
already formed sometimes taking place. Pellets of an alloy
of sodium and aluminium appear on the surface and burn with
a white light.
" These comments excited me to further research in the mat-
ter. At first, it was necessary to consider or prove whether by
melting sodium chloride with cryolite a true chemical decom-
position took place, such as Dr. Schmidt supposed. If this
were the case, the very volatile aluminium chloride must neces-
sarily be mostly driven off on melting the mixture, and at a
temperature of 700° to 1000° C. there could not be any left in
it. But an experiment in a platinum retort showed that such a
reaction positively does not occur ; for neither was any alu-
minium chloride volatilized, nor did the residue contain any,
for on treatment with water, it gave up no trace of a soluble
aluminium compound. During the melting of the mixture, acid
vapors proceeded from the retort, and a small quantity of cryo-
lite was volatilized into the neck of the retort. Dr. Klochman
has shown that cryolite always contains quartz, even colorless,
transparent pieces, which to the naked eye appear perfectly
homogeneous, showing it when examined in thin sections under
the microscope, and on melting the mineral opportunity is
given for the following reactions :
SiOa 4- 4NaF = SiF, + 2Na20,
sNa^O + Al^Fe = 6NaF + AUO,,
as is rendered probable by the appearance of delicate crystals
of alumina on the inner surface of the retort just above the
fusion. The silicon fluoride probably passes away as silico-
fluoride of sodium.
" If cryolite is fused with such metallic chlorides that really do
REDUCTION OF ALUMINIUM COMPOUNDS. 37 1
bring about a decomposition, there is never any aluminium
chloride formed in these cases, but the sodium of the cryolite is
exchanged for the other metal. Dr. O , to whom I owe this
observation, fused cryolite with calcium chloride, hoping that
aluminium chloride would distil, but obtained instead crystals
of the calcium salt of alumina-fluoric acid ; thus,
NaeAljFi, + aCaClj = 6NaCl + CajAl^Fi^,
and in like manner can be obtained the analogous strontium or
barium compounds.
" Just as erroneous as the supposed production of aluminium
chloride are the other arguments advanced by Dr. Schmidt, re-
garding the reasons why sodium could not be set free. The
self-evident premises for the propositions are lacking, viz. : that
the two bodies compared are conductors. On the contrary, I
have previously shown* that aluminium chloride and bromide,
and more certainly its fluoride, belong to the non-conductors.
It follows, then, that there can remain no doubt that on elec-
trolyzing pure cryolite, or a mixture of it, with sodium chloride,
only sodium will be set free at first, either from sodium fluoride
or the more easily decomposable sodium chloride. The pres-
ence or absence of sodium chloride is consequently, chemically,
without significance.
" Since the experiments with solid cathodes gave aluminium,
while those with molten copper did not, these results being
independent of the presence or absence of sodium chloride, the
next attempt made was to seek for the cause of the different re-
sults in the differences of temperature. It was found that when
the electrolysis takes place at a temperature about the melting
point of copper, bubbles of sodium vapor rise and burn, and any
aluminium set free is so finely divided that it is attacked and
dissolved by the cryolite. To explain this action of the cryo-
lite it is necessary to admit the formation of a lower fluoride of
aluminium and sodium, such as I have recently proven the exist-
* Chemiker Zeitung (Cothen), xi., p. 934 (1887).
372 ALUMINIUM.
ence of.* The solution of the aluminium takes place according
to the following reaction:
Al^Fe.eNaF + Al = 3 (AlF2.2NaF) .
If the electrolysis takes place at a temperature so low that the
sodium separates out as a liquid (its volatilizing point is about
900°), large globules of aluminium will be produced, on which
the cryolite seems to exert no appreciable action. Nevertheless,
the yield of aluminium is much below the theoretical quantity
set free. Since pure copper melts at 1050°, and aluminium
bronze at 800°, the copper electrodes can remain unfused in the
bath while the bronze melts off as it forms, while the tempera-
ture can be low enough to keep the sodium in the liquid state.
By mixing sodium or potassium chlorides with the cryolite, the
melting point is lowered, or at a given temperature the bath is
more fluid, and so easier to work. When there is not enough
aluminium fluoride present in the bath to utilize all the sodium
liberated, the excess of sodium may form an alloy with some
aluminium, and rising to the surface, burn to waste. Since cry-
olite always contains silica, as previously explained, the bronze
thus obtained is always rendered hard with silicon, and is not of
much value commercially.''
Hall's Process.
Although Hall's patents were not issued by the patent office
until 1889, yet they were applied for in the middle of 1886, and
a commercial-sized plant was put up to work the process in
1888. Mr. Hall really discovered the principle on which his
process is based, and made some aluminium by it, on a small
scale, in February, 1886.
*Chem. Zeit. (Cothen), xiii., p. I (1879). Hampe melted together aluminium and
sodium fluorides in the proportions of one molecule of the first to four of the second,
and obtained what is apparently a lower fluoride than cryolite, in which aluminium
cannot be otherwise than diatomic, since analysis gives it the formula AlF2.2NaF.
This salt is similar in appearance and properties to cryolite. As there are still some
doubts, however, about this compound, the above explanation of the solution of alu-
minium by the cryolite need not be accepted as final.
REDUCTION OF AI,UMINIUM COMPOUNDS. 373
The inventor of this process, Charles M. Hall, of Oberlin,
Ohio, born in 1863, is a graduate of Oberlin College, and while
yet a student spent considerable time in experimenting on iso-
lating aluminium with the electric current. Less than a year
after leaving college, he conceived the following idea, which I
quote in his own words : " It occurred to me that if I could find
some stable solvent for alumina itself, which at a reasonable
and practicable temperature would dissolve the alumina by the
mere mingling of it with the solvent and allow the alumina so
dissolved to be electrolyzed out of it, leaving the solvent unaf-
fected, this would possibly be the best process which could be
devised for the manufacture of aluminium by electrolysis."
Many different salts were tried, to see if they possessed the
property required, among them the fluorides of calcium, mag-
nesium, sodium and potassium. These latter salts were the
only ones which gave any encouraging results, but the first two
were too hard to fuse, and they all dissolved only small quan-
tities of alumina. Hall next tried cryolite, the natural com-
pound of aluminium and sodium fluorides, and found that it
melted at a red heat and readily dissolved considerable alumina.
This was on February 10, 1886. On applying the electric cur-
rent to this bath he was not immediately successful ; but, at-
tributing the failure to the presence of silica in the crucible
lining, he tried a crucible with a carbon lining, and the experi-
ment was entirely successful. This was February 23, 1886, and
on July 9, of the same year. Hall applied for patents covering
his invention.
P. L. V. Heroult, of Paris, France, had, however, apphed for
a United States patent for substantially the same process on
May 22, 1886, and the patent ofifice declared an interference
and ordered both parties to give evidence as to the date of
invention and putting into practice. Hall was able to name
February 23, 1886, as the date on which he had put his inven-
tion into practical operation, while Heroult named only the
date of his French patent for the same invention, April 23,
1886. (See p. 386.) The result of these proceedings was
374 ALUMINIUM.
that a patent covering the process was issued to Hall on April
2, 1889. (Number 400,766.) This patent has claims cover-
ing the use of the following process :
1. Dissolving alumina in a fused bath composed of the
fluorides of aluminium and a metal more electropositive than
aluminium, and then passing an electric current through the
fused mass.
2. Dissolving alumina in a fused bath composed of the
fluorides of aluminium and sodium, and then passing an
electric current, by means of a carbonaceous anode, through
the fused mass.
In the specification of the patent, it is stated that the bath
preferred as a solvent contains :
Sodium fluoride 33.2 per cent.
Aluminium fluoride 66.8 per cent.
represented by the formula AlFj.NaF. A convenient method
of forming this bath consists in adding to the mineral cryolite
80.3 per cent, of its weight of aluminium fluoride, according to
the formula :
AlFs.sNaF + 2AIF3 = sCAlFs.NaF).
It is further stated that the bath may be fused in a crucible
or melting pot of iron or steel having a carbon lining, that the
positive electrode may be of carbon, copper, platinum or any
other suitable material, and the negative electrode a carbon
rod or the carbon lining of the bath. When the positive
electrode is carbon it is gradually consumed by the oxygen
liberated, but when copper is used a coating of copper oxide
is at once formed on it, which protects it from further oxidation
and causes free oxygen to be liberated. The tension required
to operate a bath is stated as 4 to 6 volts.
The above description may be taken as summarizing Hall's
process as developed by him at the date of application for his
patent, July, 1886. It is the writer's opinion that credit should
be given to both Hall and Heroult for originating this inven-
REDUCTION OF ALUMINIUM COMPOUNDS. 375
tion, as the principle was discovered independently by each at
very nearly the same time ; but in the subsequent development
and practical application of the invention, Hall in America
clearly outstripped Heroult in Europe.
Several other patents were subsequently applied for by Hall,
covering modifications of the original process, and these were
all issued with the original patent in 1889.* One covers the
use of a potassium-aluminium fluoride, AIF3.KF, instead of the
corresponding sodium salt, since it is much more fusible.
Also the addition of lithium fluoride to this salt. Another
covers the use of calcium and aluminium fluorides to form the
bath, such as 2AlF3.CaF2 or 2AlF3.3CaF2. Since this bath is of
higher specific gravity than molten aluminium, it is recom-
mended to add to it enough of the salt AIF3.KF to lower the
specific gravity below that of the aluminium. This is unneces-
sary if alloys of aluminium are to be made, in which case the
metal to be alloyed is made the negative electrode and the
alloy formed will be sufficiently heavy to sink. For making
alloys, the addition of barium fluoride to the bath is recom-
mended, as its high specific gravity is no inconvenience and it
is more fusible than the calcium or strontium fluorides. In
another of these patents, the bath specified has the formula
2(AlF3.3NaF) + aAlFj-CaFj, being made by melting together
cryolite, aluminium fluoride and fluorspar. When the bath
becomes clogged, by the settling out of a mushy deposit which
stops the current, the addition of 3 or 4 per cent, of anhydrous
calcium chloride is recommended as clearing or liquefying the
bath ; this addition is also said to lessen the disintegration of
the carbon anodes used.
As at present conducted, the process is worked according to
the original patent applied for in 1886, it having been found
that almost all the difficulties which the subsequent modifica-
tions were designed to overcome are entirely obviated by regu-
lar working on a large scale. It has been concluded from
* Numbers 400,664; 400,665; 400,666; 400,667; 400,766.
376 ALUMINIUM.
subsequent experience that almost all the difficulties met at
first were the results of the varying composition of the bath
and its irregular temperature, and were inherent in attempts to
work on a small scale.
From June, 1887, to the middle of 1888, Mr. Hall experi-
mented on his process at the Cowles' Bros, works at Lockport,
N. Y. His results here, working on a small scale, were not
sufficiently economical to induce that company to continue the
work. Mr. Hall, however, was confident that if the process
could be started on a large scale, aluminium could be made at
a cost very much below its selling price at that time. Leaving
Lockport, Mr. Hall went to Pittsburgh, and there, through the
influence of Mr. Romaine C. Cole, was successful in interesting
several capitalists, who contributed $20,000 in cash to put up a
works, and in September, 1888, organized the Pittsburgh Reduc-
tion Company, with a capital stock of $1,000,000. The con-
struction of the plant was immediately begun, and in Novem-
ber, 1888, aluminium was being produced at the rate of 50
pounds per day, which found a ready sale at $5 per pound,
leaving a handsome profit.
This plant was situated in Pittsburgh, and was operated by
steam-power, using coal for fuel. The machinery consisted of
two ordinary tubular boilers of sixty horse-power each, and a
Westinghouse " automatic " engine of 125 horse-power, running
two shunt-wound Westinghouse dynamos. These dynamos,
running at 1,000 revolutions, gave each a current of 1,000
amperes at 25 volts tension, and being coupled in parallel gave
a current of 2,000 amperes at full speed, or an average of 1,700
to 1,800 amperes at 16 volts on steady runs. This current was
passed through two reducing pots, coupled in series. These
pots were of cast-iron, 24 inches long, 16 inches wide and 20
inches deep, lined inside with a layer of hard-baked carbon 3
inches thick. From a copper bar above were suspended, by
^ inch copper rods, 6 to 10 three-inch carbon cylinders, each
originally 15 inches long. Each pot. held 200 to 300 pounds
of the electrolyte.
REDUCTION OF ALUMINIUM COMPOUNDS. 377
It was found that with apparatus and current of this size,
outside heating was not necessary; the heat generated by the
passage of the current being sufficient to keep the bath fused
at the proper temperature. Larger pots have since been used,
which will be described later, but as the operation in them is
exactly similar to that in the smaller ones, we will describe the
process at once.
The carbon lining of the pot forms the negative electrode,
connection being made to the iron casing. The fluoride salts
to form the bath are placed in the bottom of the cavity, the
carbon positive electrodes lowered until they touch the carbon
lining, and the current turned on. After a few minutes the
salt is melted and when red-hot in the vicinity of each carbon,
more salt is thrown around the carbons, or each carbon moved
up a little. In an hour or two sufficient salt has been melted to
form the bath, and the carbons have been brought out of direct
contact with the lining. The bath is now ready to dissolve
alumina, which is first sprinkled on top of the bath, and after
it has become hot and perfectly dry is stirred in.
The fumes which were arising from the decomposition of the
fluorine salts immediately cease, the voltage absorbed by the
bath falls, the number of amperes passing increases, and the
electrolysis of the dissolved alumina commences at once.
Powdered carbon (the stub ends of electrodes ground up) is
now placed on top of the bath in a layer about an inch thick,
serving to keep in the heat and so reduce the loss by radiation.
The carbon electrodes are clamped to a copper bar extending
the whole length of the pot (see Fig. 38), and if one part of
the bath becomes cooler than it should be, the carbons are
crowded together at that point and soon heat it up. In prac-
tice, the ends of the carbons are kept about 0.5 to i inch from
the lining, and each one carries about 250 to 300 amperes. If
more current than this passes through a carbon, as might happen
if it short-circuited, the copper rod becomes red-hot at its con-
nection with the carbon. As soon as this is observed, the
workman raises it slightly and so stops the extra current. The
378
ALUMINIUM.
carbons wear down gradually until only 3 or 4 inches long (the
depth of liquid bath is not over 6 inches) and must then be
replaced. The consumption of carbons in regular running is
less than one pound per pound of aluminium produced, show-
ing that they are burnt according to the reaction
AI.O, + 3C = 2AI + 3CO.
in which 102 parts of alumina would require 36 parts of car-
bon to combine with its oxygen, producing 54 parts of metal.
Fig. 38.
Theoretically, therefore, there is required || or ^ of a pound
of carbon to i pound of aluminium produced. The smal'l
amount over this actually used is consumed by the air with
which they inevitably come in contact.
In these small pots, a tension of 8 volts is required to oper-
ate each, at an amperage of 1800. If the voltage rises to 10
or more, it indicates that the alumina in the bath has become
exhausted, as is also shown by dense, irritating fluoride fumes.
REDUCTION OF ALUMINIUM COMPOUNDS. 3/9
The workman at once stirs in some of the alumina which is
always kept on top of the carbon covering, and the voltage
immediately falls. A delicate electrical instrument, set to a
certain voltage, gives immediate notice to the workman when
the bath is " out of ore." In regular working no fumes arise,
the carbon covering entirely conceals the red-hot fluid bath
beneath, and one can only convince himself that the bath is
really in operation by approaching and noticing the heat
radiated. When aluminium has accumulated for several hours,
it is ladled out with iron ladles well-rubbed with chalk or
plumbago. This operation gives rise to some fumes, and also
causes some of the electrolyte to be dipped out with the metal.
It has been suggested that a tap-hole should be provided, but
there was found great difficulty in keeping the pot tight when
this was tried, and the expedient of syphoning out the metal
has been found more practicable.
The crude ingots thus poured are re-melted in large crucibles ;
the re-melting plant is shown in Fig. 39.
The alumina used in this plant was from the German manu-
turer, Bergius, at Goldschmeiden, near Breslau, Silesia. As im-
ported, it contained about 33 per cent, of moisture, which is
driven off in a drying furnace. The cost of alumina was, in
1890, five cents a pound delivered in Pittsburgh, which would
make the dried alumina cost 7.5 cents per pound plus the cost
of calcining, which is not over 0.5 cent. If absolutely pure,
alumina should contain 52.94 per cent, of aluminium, but as
this calcined alumina usually contains about i per cent, of im-
purities, chiefly silica, there is only a little over 52 per cent, of
metal in it. An accurate account of several months' running
showed that the Hall process extracts a fraction over 50 per
cent, of metal from it. The alumina to furnish one pound of
aluminium therefore cost in 1890 about 16 cents. Since then,
the alumina is calcined in Germany before shipment, saving in
freight and customs dues, and can probably be laid down now
in New York at S cents per pound, making a cost of 10 cents
per pound of aluminium. There is, besides this, a small waste
38o
ALUMINIUM.
of bath material, which costs in the neighborhood of 7 cents per
pound to make, but since this does not in actual running
amount to over 2 pounds per 100 pounds of aluminium pro-
duced, this item of expense is quite small.
The output of these small pots was about one pound of
metal an hour from each, and they were kept in continued ope-
ration for several weeks at a time. If pure alumina is used,
Fig. 39.
,, "^^-^ /W''.
pure aluminium is produced ; that made from Bergius' alumina
averaging over 98 per cent. pure.
When a bath has been put into operation, the metal first
produced is contaminated with the silicon and iron present in
the bath material, but in a few days these are completely elim-
inated, and the bath material is almost chemically pure save for
the impurities introduced in the alumina.
If calcined, selected raw bauxite is used in the pots, the
metal produced averages 94 to 96 per cent, pure, and is sold for
REDUCTION OF ALUMINIUM COMPOUNDS. 38 1
use in iron and steel. Two analyses of such second quality-
metal gave :
Aluminium 94.16 9S'93
Silicon 4.36 2.01
Iron 1.48 2.06
As the material used only costs about i cent per pound
ready to put into the pots, and about 2^ pounds make one of
metal, this second quality metal costs about 7 cents less per
pound than the first quality.
An estimate of the cost of producing aluminium in this plant
in 1889, at the rate of fifty pounds per day, is as follows:
100 lbs. calcined alumina @ 8 cts =. $8.00
Fluorides for bath @ 7 cts = .50
Carbons = i.oo
50 horse-power engine = 15.00
2 engineers @ $3.00 per diem = 6.00
6 workmen @ ;j2.oo " = 12.00
Superintendence, office expenses, etc .= 10.00
Interest on plant, rent, etc ^ 7.50
Cost of about 50 lbs. of aluminium $60.00
In the early part of 1890 the plant was greatly enlarged.
The additions consisted of three Babcock and Wilcox boilers of
200 horse-power each, fired by natural gas ; two 200 Jiorse-
power Westinghouse compound engines ; two shunt-wound
Westinghouse dynamos running 325 revolutions per minute,
connected in parallel and giving a total current of 5000 amperes
at 50 volts tension. The conductors for this current were two
copper bars, 6 inches by 0.5 inch, giving a total cross-section
of 6 square inches. This gives a little over 800 amperes per
square inch section. This current operated five large pots con-
nected in series, averaging 9 volts to a pot. These large pots
are of one-quarter inch wrought iron, 5 feet long, 2% feet wide
and 2 feet deep, with a carbon lining 4 to 6 inches thick, and
supported on bricks to keep the bottom cool. Above are two
copper bars to which a double row of carbon electrodes are
clamped, there being 10 on each row or 20 in all. Each of
382 ALUMINIUM.
these pots produced 60 to 70 pounds of aluminium a day, mak-
ing the production of the entire plant in 1890 about 400
pounds per day. The cost of aluminium, working on this scale,
could scarcely have been over $0.75 per pound, since the
metal made here was sold during 1891 for $1.00 per pound.
During 1891, in order to obtain room to extend and cheapen
fuel, the entire plant was moved to New Kensington, Pa., on the
Allegheny River 18 miles from Pittsburgh. At this place the
capacity of the plant has been greatly increased, there being ap-
proximately 1500 horse-power employed, and the output having
been increased to lOOO pounds per day in 1893 and to nearly
2000 pounds per day in 1894. Since the selling price has been
reduced to $0.50 per pound, it is evident that the present
cost cannot be much over $0.40, if so high. Captain A. E.
Hunt, president of the company, is authority for saying that as
the process is operated on an increasing scale, and more exper-
ience is had in running it, the cost in the future will approxi-
mate $0.20 per pound, the lowest limit by this process.
In July, 1890, a plant to work Hall's process was put into
operation at Patricoft, Lancashire, England, with a capacity of
about 300 pounds of aluminium a day. This plant was in
operation until 1894, when competition from Switzerland com-
pelled it to close.
During 1894, the United States Company have been con-
structing a larger plant at Niagara Falls, being furnished power
by the Niagara Falls Power Co. A contract has been made to
take 6000 horse-power, and the plant, so far constructed, is as
follows : *
A 5000 horse-power turbine, in the Power Company's power-
house, runs a 5000 horse-power, low frequency, alternating
current Tesla dynamo. This machine, at full speed, gives two
currents of 2500 volts by 775 amperes each, alternating 50 times
per second. The exciting circuit is continuous, obtained from
the main circuit by a rotary transformer, and amounts to only
0.2 per cent, of the main current. The total current of 2500
*This plant was put into operation on August 26, 1895.
REDUCTION OF ALUMINIUM COMPOUNDS. 383
volts by 1550 amperes is conducted through an underground
tunnel one-half mile to the aluminium works, through copper
rope conductors, with a total section of 4.3 square inches, with
a drop in potential of 12 volts. At the works, the current is
first passed through a set of stationary transformers, each of
250 horse-power, in which the current is reduced from 2487
volts to 115 volts. The alternating current of 115 volts next
passes to rotary transformers, each of 500 horse-power and
taking the current from two stationary transformers. In these
the alternating current of 115 volts is changed to a direct cur-
rent of 160 volts, the quantity of current furnished by each
rotary transformer being 2500 amperes. These currents of
2500 amperes by 160 volts are conducted to the pot room on
copper bars with 1.25 square inch section, each passing through
a separate switch-board, on which are shunt ammeters and vol-
meters, and then passed to the pots. The buildings are all of
iron, the main reduction room being 180 by 85 feet.
It is not difScult to estimate what the output of the two works
will be. At Pittsburgh each horse-power of electrical energy
produced about 1.2 pounds of aluminium per day, at which rate
a 5000 horse-power plant should make 6000 pounds, equiva-
lent in round numbers to 1000 tons a year, the present value of
which is $1,000,000.
Reactions and efficiency of the process. — Taking the first small
plant, a current of 1800 amperes in two vats should theoreti-
cally produce 56.4 pounds of aluminium per day. As 50
pounds were obtained, on an average, the efficiency shown in
this direction is nearly 90 percent. As only about 2.5 volts
out of the 9 volts absorbed by the bath, is used in decomposing
the alumina, wc have about 30 per cent, of the current thus
utilized. The efficiency over all is therefore 90 per cent, of 30
per cent.=27 per cent. This means that the work of separat-
ing aluminium from oxygen represents 27 per cent, of the actual
energy of the current. The difference between 9 and 2.5, or
6.5 volts, is absorbed in the conduction resistance of the bath,
being converted into heat. This would give a heat develop-
384 ALUMINIUM.
ment of 6.25 X 1800x0.00024= 2.7 calories per second, or
9720 calories per hour. To this we may add the heat of
oxidation of the carbon to carbonic oxide, and we have the
total heat generated in the bath. A balance would show as
follows :
Heat Developed per Hour.
By electrical resistances 9720 calories.
Oxidation of the carbon 960 "
Total 10680 "
Heat Distribution per Hour.
Heating 2 pounds alumina to 900° C 250 calories.
Withdrawn with the aluminium 17S "
Lost by radiation and conduction 10265 "
Total 10680
As to the real reaction in the bath, by which aluminium is
liberated, several metallurgists have taken the ground that the
aluminium fluoride present is the substance primarily disso-
ciated by the current, and that the fluorine set free at the anode
immediately acts on the alumina present in solution and re-
forms aluminium fluoride, liberating oxygen, which then unites
with the carbon. According to this view the reactions are
2AIF3 + Current = 2AI + 6F.
MO3 + 6F = 2AIF, + 3O.
3C + 3O = 3CO.
This theory must assume either one of two things ; first,
that the alumina added never becomes an integral part of the
bath, but remains suspended mechanically; or, second, that if
the alumina really is part of the bath, it is a stronger com-
pound than aluminium fluoride, and therefore, the current
decomposes the latter. This theory, however, involves several
contradictions. If, for instance, alumina is really a stronger
compound than aluminium fluoride, how could the gaseous
REDUCTION OF ALUMINIUM COMPOUNDS. 385
fluorine decompose alumina, forming aluminium fluoride?
Since gaseous fluorine can decompose alumina, as was proven
by Moissan, it follows that alumina is therefore a weaker com-
pound than aluminium fluoride, and that when an electric cur-
rent is passed through a bath containing these two compounds
the alumina is necessarily the first to be decomposed. The
only refuge left for this theory is, then, to maintain that the
alumina is not truly dissolved in the bath, but is only me-
chanically suspended. This, however, is contrary to the way
in which the bath behaves. Absorption of the fluorine could
not possibly be as perfect in that case as it really is in practice.
Besides, an experiment of Mr. Hall's settles the case, it seems
to me, beyond question. On passing the current through an
anode of clean copper, it becomes immediately coated with a
layer of copper oxide. If fluorine were at all set free, it would
be liberated in immediate contact with the anode, and copper
fluoride must necessarily have been formed ; but no trace of
that salt is observed. It thus appears impossible to me that
the electric current does anything but dissociate oxygen from
aluminium.
It has been suggested that the alumina is dissolved in the
bath by forming aluminium oxy-fluoride, and that this is the
substance electrolyzed. This may or may not be true, but there
is up to the present time no positive proof for the theory, and
several circumstances against it. No chemist has as yet iso-
lated and analyzed any such salt. If such salt is formed, the
larger the proportion of aluminium fluoride in the bath, the
more alumina it ought to dissolve. But cryolite contains 40
per cent, of aluminium fluoride, and dissolves at least 25 per
cent, of its weight of alumina to a clear solution, while the salt
AlFg.NaF, containing 66 per cent, of aluminium fluoride, and
made by adding aluminum fluoride to cryolite, dissolves barely
10 per cent. Further, no evolution of heat 
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